diff --git a/x-pack/plugins/cases/public/components/case_view/components/case_view_activity.tsx b/x-pack/plugins/cases/public/components/case_view/components/case_view_activity.tsx
index 63be7009f8c15..07cf815555f61 100644
--- a/x-pack/plugins/cases/public/components/case_view/components/case_view_activity.tsx
+++ b/x-pack/plugins/cases/public/components/case_view/components/case_view_activity.tsx
@@ -58,7 +58,8 @@ export const CaseViewActivity = ({
     [caseData.assignees]
   );
 
-  const uidsToRetrieve = uniq([...(userActionsData?.profileUids ?? []), ...assignees]);
+  const userActionProfileUids = Array.from(userActionsData?.profileUids.values() ?? []);
+  const uidsToRetrieve = uniq([...userActionProfileUids, ...assignees]);
 
   const { data: userProfiles, isLoading: isLoadingUserProfiles } = useBulkGetUserProfiles({
     uids: uidsToRetrieve,
diff --git a/x-pack/plugins/cases/public/components/user_actions/assignees.test.tsx b/x-pack/plugins/cases/public/components/user_actions/assignees.test.tsx
index f27721fa5c04a..57cde43c9fee6 100644
--- a/x-pack/plugins/cases/public/components/user_actions/assignees.test.tsx
+++ b/x-pack/plugins/cases/public/components/user_actions/assignees.test.tsx
@@ -12,158 +12,219 @@ import { render, screen } from '@testing-library/react';
 import { Actions } from '../../../common/api';
 import { elasticUser, getUserAction } from '../../containers/mock';
 import { TestProviders } from '../../common/mock';
-import { createAssigneesUserActionBuilder } from './assignees';
+import { createAssigneesUserActionBuilder, shouldAddAnd, shouldAddComma } from './assignees';
 import { getMockBuilderArgs } from './mock';
 
 jest.mock('../../common/lib/kibana');
 jest.mock('../../common/navigation/hooks');
 
 describe('createAssigneesUserActionBuilder', () => {
-  const builderArgs = getMockBuilderArgs();
-
-  beforeEach(() => {
-    jest.clearAllMocks();
-  });
-
-  it('renders assigned users', () => {
-    const userAction = getUserAction('assignees', Actions.add, {
-      createdBy: {
-        // damaged_raccoon uid
-        profileUid: 'u_J41Oh6L9ki-Vo2tOogS8WRTENzhHurGtRc87NgEAlkc_0',
-      },
+  describe('shouldAddComma', () => {
+    it('returns false if there are only 2 items', () => {
+      expect(shouldAddComma(0, 2)).toBeFalsy();
     });
-    const builder = createAssigneesUserActionBuilder({
-      ...builderArgs,
-      userAction,
-    });
-
-    const createdUserAction = builder.build();
-    render(
-      <TestProviders>
-        <EuiCommentList comments={createdUserAction} />
-      </TestProviders>
-    );
-
-    expect(screen.getByText('assigned')).toBeInTheDocument();
-    expect(screen.getByText('themselves,')).toBeInTheDocument();
-    expect(screen.getByText('Physical Dinosaur')).toBeInTheDocument();
 
-    expect(screen.getByTestId('ua-assignee-physical_dinosaur')).toContainElement(
-      screen.getByText('and')
-    );
-  });
-
-  it('renders unassigned users', () => {
-    const userAction = getUserAction('assignees', Actions.delete, {
-      createdBy: {
-        // damaged_raccoon uid
-        profileUid: 'u_J41Oh6L9ki-Vo2tOogS8WRTENzhHurGtRc87NgEAlkc_0',
-      },
-    });
-    const builder = createAssigneesUserActionBuilder({
-      ...builderArgs,
-      userAction,
+    it('returns false it is the last items', () => {
+      expect(shouldAddComma(2, 3)).toBeFalsy();
     });
-
-    const createdUserAction = builder.build();
-    render(
-      <TestProviders>
-        <EuiCommentList comments={createdUserAction} />
-      </TestProviders>
-    );
-
-    expect(screen.getByText('unassigned')).toBeInTheDocument();
-    expect(screen.getByText('themselves,')).toBeInTheDocument();
-    expect(screen.getByText('Physical Dinosaur')).toBeInTheDocument();
-
-    expect(screen.getByTestId('ua-assignee-physical_dinosaur')).toContainElement(
-      screen.getByText('and')
-    );
   });
 
-  it('renders a single assigned user', () => {
-    const userAction = getUserAction('assignees', Actions.add, {
-      payload: {
-        assignees: [
-          // only render the physical dinosaur
-          { uid: 'u_A_tM4n0wPkdiQ9smmd8o0Hr_h61XQfu8aRPh9GMoRoc_0' },
-        ],
-      },
+  describe('shouldAddAnd', () => {
+    it('returns false if there is only 1 item', () => {
+      expect(shouldAddAnd(0, 1)).toBeFalsy();
     });
-    const builder = createAssigneesUserActionBuilder({
-      ...builderArgs,
-      userAction,
-    });
-
-    const createdUserAction = builder.build();
-    render(
-      <TestProviders>
-        <EuiCommentList comments={createdUserAction} />
-      </TestProviders>
-    );
 
-    expect(screen.getByText('Physical Dinosaur')).toBeInTheDocument();
-    expect(screen.queryByText('themselves,')).not.toBeInTheDocument();
-    expect(screen.queryByText('and')).not.toBeInTheDocument();
+    it('returns false it is not the last items', () => {
+      expect(shouldAddAnd(1, 3)).toBeFalsy();
+    });
   });
 
-  it('renders a single assigned user that is themselves using matching profile uids', () => {
-    const userAction = getUserAction('assignees', Actions.add, {
-      createdBy: {
-        ...elasticUser,
-        profileUid: 'u_J41Oh6L9ki-Vo2tOogS8WRTENzhHurGtRc87NgEAlkc_0',
-      },
-      payload: {
-        assignees: [
-          // only render the damaged raccoon which is the current user
-          { uid: 'u_J41Oh6L9ki-Vo2tOogS8WRTENzhHurGtRc87NgEAlkc_0' },
-        ],
-      },
-    });
-    const builder = createAssigneesUserActionBuilder({
-      ...builderArgs,
-      userAction,
+  describe('component', () => {
+    const builderArgs = getMockBuilderArgs();
+
+    beforeEach(() => {
+      jest.clearAllMocks();
     });
 
-    const createdUserAction = builder.build();
-    render(
-      <TestProviders>
-        <EuiCommentList comments={createdUserAction} />
-      </TestProviders>
-    );
+    it('renders assigned users', () => {
+      const userAction = getUserAction('assignees', Actions.add, {
+        createdBy: {
+          // damaged_raccoon uid
+          profileUid: 'u_J41Oh6L9ki-Vo2tOogS8WRTENzhHurGtRc87NgEAlkc_0',
+        },
+      });
+      const builder = createAssigneesUserActionBuilder({
+        ...builderArgs,
+        userAction,
+      });
+
+      const createdUserAction = builder.build();
+      render(
+        <TestProviders>
+          <EuiCommentList comments={createdUserAction} />
+        </TestProviders>
+      );
+
+      expect(screen.getByText('assigned')).toBeInTheDocument();
+      expect(screen.getByText('themselves')).toBeInTheDocument();
+      expect(screen.getByText('Physical Dinosaur')).toBeInTheDocument();
+
+      expect(screen.getByTestId('ua-assignee-physical_dinosaur')).toContainElement(
+        screen.getByText('and')
+      );
+    });
 
-    expect(screen.getByText('themselves')).toBeInTheDocument();
-    expect(screen.queryByText('Physical Dinosaur')).not.toBeInTheDocument();
-    expect(screen.queryByText('and')).not.toBeInTheDocument();
-  });
+    it('renders assigned users with a comma', () => {
+      const userAction = getUserAction('assignees', Actions.add, {
+        createdBy: {
+          // damaged_raccoon uid
+          profileUid: 'u_J41Oh6L9ki-Vo2tOogS8WRTENzhHurGtRc87NgEAlkc_0',
+        },
+        payload: {
+          assignees: [
+            // These values map to uids in x-pack/plugins/cases/public/containers/user_profiles/api.mock.ts
+            { uid: 'u_J41Oh6L9ki-Vo2tOogS8WRTENzhHurGtRc87NgEAlkc_0' },
+            { uid: 'u_A_tM4n0wPkdiQ9smmd8o0Hr_h61XQfu8aRPh9GMoRoc_0' },
+            { uid: 'u_9xDEQqUqoYCnFnPPLq5mIRHKL8gBTo_NiKgOnd5gGk0_0' },
+          ],
+        },
+      });
+      const builder = createAssigneesUserActionBuilder({
+        ...builderArgs,
+        userAction,
+      });
+
+      const createdUserAction = builder.build();
+      render(
+        <TestProviders>
+          <EuiCommentList comments={createdUserAction} />
+        </TestProviders>
+      );
+
+      expect(screen.getByText('assigned')).toBeInTheDocument();
+      expect(screen.getByText('themselves,')).toBeInTheDocument();
+      expect(screen.getByText('Physical Dinosaur')).toBeInTheDocument();
+
+      expect(screen.getByTestId('ua-assignee-physical_dinosaur')).toContainElement(
+        screen.getByText(',')
+      );
+
+      expect(screen.getByText('Wet Dingo')).toBeInTheDocument();
+      expect(screen.getByTestId('ua-assignee-wet_dingo')).toContainElement(screen.getByText('and'));
+    });
 
-  it('renders a single assigned user that is themselves using matching usernames', () => {
-    const userAction = getUserAction('assignees', Actions.add, {
-      createdBy: {
-        ...elasticUser,
-        username: 'damaged_raccoon',
-      },
-      payload: {
-        assignees: [
-          // only render the damaged raccoon which is the current user
-          { uid: 'u_J41Oh6L9ki-Vo2tOogS8WRTENzhHurGtRc87NgEAlkc_0' },
-        ],
-      },
+    it('renders unassigned users', () => {
+      const userAction = getUserAction('assignees', Actions.delete, {
+        createdBy: {
+          // damaged_raccoon uid
+          profileUid: 'u_J41Oh6L9ki-Vo2tOogS8WRTENzhHurGtRc87NgEAlkc_0',
+        },
+      });
+      const builder = createAssigneesUserActionBuilder({
+        ...builderArgs,
+        userAction,
+      });
+
+      const createdUserAction = builder.build();
+      render(
+        <TestProviders>
+          <EuiCommentList comments={createdUserAction} />
+        </TestProviders>
+      );
+
+      expect(screen.getByText('unassigned')).toBeInTheDocument();
+      expect(screen.getByText('themselves')).toBeInTheDocument();
+      expect(screen.getByText('Physical Dinosaur')).toBeInTheDocument();
+
+      expect(screen.getByTestId('ua-assignee-physical_dinosaur')).toContainElement(
+        screen.getByText('and')
+      );
     });
-    const builder = createAssigneesUserActionBuilder({
-      ...builderArgs,
-      userAction,
+
+    it('renders a single assigned user', () => {
+      const userAction = getUserAction('assignees', Actions.add, {
+        payload: {
+          assignees: [
+            // only render the physical dinosaur
+            { uid: 'u_A_tM4n0wPkdiQ9smmd8o0Hr_h61XQfu8aRPh9GMoRoc_0' },
+          ],
+        },
+      });
+      const builder = createAssigneesUserActionBuilder({
+        ...builderArgs,
+        userAction,
+      });
+
+      const createdUserAction = builder.build();
+      render(
+        <TestProviders>
+          <EuiCommentList comments={createdUserAction} />
+        </TestProviders>
+      );
+
+      expect(screen.getByText('Physical Dinosaur')).toBeInTheDocument();
+      expect(screen.queryByText('themselves,')).not.toBeInTheDocument();
+      expect(screen.queryByText('and')).not.toBeInTheDocument();
     });
 
-    const createdUserAction = builder.build();
-    render(
-      <TestProviders>
-        <EuiCommentList comments={createdUserAction} />
-      </TestProviders>
-    );
+    it('renders a single assigned user that is themselves using matching profile uids', () => {
+      const userAction = getUserAction('assignees', Actions.add, {
+        createdBy: {
+          ...elasticUser,
+          profileUid: 'u_J41Oh6L9ki-Vo2tOogS8WRTENzhHurGtRc87NgEAlkc_0',
+        },
+        payload: {
+          assignees: [
+            // only render the damaged raccoon which is the current user
+            { uid: 'u_J41Oh6L9ki-Vo2tOogS8WRTENzhHurGtRc87NgEAlkc_0' },
+          ],
+        },
+      });
+      const builder = createAssigneesUserActionBuilder({
+        ...builderArgs,
+        userAction,
+      });
+
+      const createdUserAction = builder.build();
+      render(
+        <TestProviders>
+          <EuiCommentList comments={createdUserAction} />
+        </TestProviders>
+      );
+
+      expect(screen.getByText('themselves')).toBeInTheDocument();
+      expect(screen.queryByText('Physical Dinosaur')).not.toBeInTheDocument();
+      expect(screen.queryByText('and')).not.toBeInTheDocument();
+    });
 
-    expect(screen.getByText('themselves')).toBeInTheDocument();
-    expect(screen.queryByText('Physical Dinosaur')).not.toBeInTheDocument();
-    expect(screen.queryByText('and')).not.toBeInTheDocument();
+    it('renders a single assigned user that is themselves using matching usernames', () => {
+      const userAction = getUserAction('assignees', Actions.add, {
+        createdBy: {
+          ...elasticUser,
+          username: 'damaged_raccoon',
+        },
+        payload: {
+          assignees: [
+            // only render the damaged raccoon which is the current user
+            { uid: 'u_J41Oh6L9ki-Vo2tOogS8WRTENzhHurGtRc87NgEAlkc_0' },
+          ],
+        },
+      });
+      const builder = createAssigneesUserActionBuilder({
+        ...builderArgs,
+        userAction,
+      });
+
+      const createdUserAction = builder.build();
+      render(
+        <TestProviders>
+          <EuiCommentList comments={createdUserAction} />
+        </TestProviders>
+      );
+
+      expect(screen.getByText('themselves')).toBeInTheDocument();
+      expect(screen.queryByText('Physical Dinosaur')).not.toBeInTheDocument();
+      expect(screen.queryByText('and')).not.toBeInTheDocument();
+    });
   });
 });
diff --git a/x-pack/plugins/cases/public/components/user_actions/assignees.tsx b/x-pack/plugins/cases/public/components/user_actions/assignees.tsx
index 0e16184634a4a..e0a499df05633 100644
--- a/x-pack/plugins/cases/public/components/user_actions/assignees.tsx
+++ b/x-pack/plugins/cases/public/components/user_actions/assignees.tsx
@@ -42,11 +42,11 @@ const FormatListItem: React.FC<{
 };
 FormatListItem.displayName = 'FormatListItem';
 
-const shouldAddComma = (index: number, arrayLength: number) => {
-  return arrayLength > 0 && index !== arrayLength - 1;
+export const shouldAddComma = (index: number, arrayLength: number) => {
+  return arrayLength > 2 && index !== arrayLength - 1;
 };
 
-const shouldAddAnd = (index: number, arrayLength: number) => {
+export const shouldAddAnd = (index: number, arrayLength: number) => {
   return arrayLength > 1 && index === arrayLength - 1;
 };
 
diff --git a/x-pack/plugins/cases/public/containers/use_get_case_user_actions.test.tsx b/x-pack/plugins/cases/public/containers/use_get_case_user_actions.test.tsx
index cb39b4e7247d5..c97e1a8668b1d 100644
--- a/x-pack/plugins/cases/public/containers/use_get_case_user_actions.test.tsx
+++ b/x-pack/plugins/cases/public/containers/use_get_case_user_actions.test.tsx
@@ -104,10 +104,38 @@ describe('useGetCaseUserActions', () => {
 
         await waitFor(() => {
           expect(result.current.data?.profileUids).toMatchInlineSnapshot(`
-            Array [
+            Set {
               "u_J41Oh6L9ki-Vo2tOogS8WRTENzhHurGtRc87NgEAlkc_0",
               "u_A_tM4n0wPkdiQ9smmd8o0Hr_h61XQfu8aRPh9GMoRoc_0",
-            ]
+            }
+          `);
+        });
+      });
+    });
+
+    it('ignores duplicate uids', async () => {
+      jest
+        .spyOn(api, 'getCaseUserActions')
+        .mockReturnValue(
+          Promise.resolve([
+            ...caseUserActions,
+            getUserAction('assignees', Actions.add),
+            getUserAction('assignees', Actions.add),
+          ])
+        );
+
+      await act(async () => {
+        const { result } = renderHook<string, UseGetCaseUserActions>(
+          () => useGetCaseUserActions(basicCase.id, basicCase.connector.id),
+          { wrapper }
+        );
+
+        await waitFor(() => {
+          expect(result.current.data?.profileUids).toMatchInlineSnapshot(`
+            Set {
+              "u_J41Oh6L9ki-Vo2tOogS8WRTENzhHurGtRc87NgEAlkc_0",
+              "u_A_tM4n0wPkdiQ9smmd8o0Hr_h61XQfu8aRPh9GMoRoc_0",
+            }
           `);
         });
       });
@@ -128,10 +156,10 @@ describe('useGetCaseUserActions', () => {
 
         await waitFor(() => {
           expect(result.current.data?.profileUids).toMatchInlineSnapshot(`
-            Array [
+            Set {
               "u_J41Oh6L9ki-Vo2tOogS8WRTENzhHurGtRc87NgEAlkc_0",
               "u_A_tM4n0wPkdiQ9smmd8o0Hr_h61XQfu8aRPh9GMoRoc_0",
-            ]
+            }
           `);
         });
       });
diff --git a/x-pack/plugins/cases/public/containers/use_get_case_user_actions.tsx b/x-pack/plugins/cases/public/containers/use_get_case_user_actions.tsx
index 04448612ce481..1d36521d0b6f4 100644
--- a/x-pack/plugins/cases/public/containers/use_get_case_user_actions.tsx
+++ b/x-pack/plugins/cases/public/containers/use_get_case_user_actions.tsx
@@ -209,14 +209,16 @@ export const getPushedInfo = (
 };
 
 export const getProfileUids = (userActions: CaseUserActions[]) => {
-  const uids = userActions.reduce<string[]>((acc, userAction) => {
+  const uids = userActions.reduce<Set<string>>((acc, userAction) => {
     if (userAction.type === ActionTypes.assignees) {
       const uidsFromPayload = userAction.payload.assignees.map((assignee) => assignee.uid);
-      acc.push(...uidsFromPayload);
+      for (const uid of uidsFromPayload) {
+        acc.add(uid);
+      }
     }
 
     return acc;
-  }, []);
+  }, new Set());
 
   return uids;
 };