diff --git a/x-pack/plugins/alerting/server/integration_tests/__snapshots__/serverless_upgrade_and_rollback_checks.test.ts.snap b/x-pack/plugins/alerting/server/integration_tests/__snapshots__/serverless_upgrade_and_rollback_checks.test.ts.snap
index 1d91422077554..c84a3565d48f6 100644
--- a/x-pack/plugins/alerting/server/integration_tests/__snapshots__/serverless_upgrade_and_rollback_checks.test.ts.snap
+++ b/x-pack/plugins/alerting/server/integration_tests/__snapshots__/serverless_upgrade_and_rollback_checks.test.ts.snap
@@ -3188,6 +3188,12 @@ Object {
                                 },
                                 "name": "custom",
                               },
+                              Object {
+                                "args": Object {
+                                  "method": [Function],
+                                },
+                                "name": "custom",
+                              },
                             ],
                             "type": "string",
                           },
@@ -5627,6 +5633,12 @@ Object {
                   },
                   "name": "custom",
                 },
+                Object {
+                  "args": Object {
+                    "method": [Function],
+                  },
+                  "name": "custom",
+                },
               ],
               "type": "string",
             },
diff --git a/x-pack/plugins/observability_solution/observability/server/lib/rules/custom_threshold/register_custom_threshold_rule_type.ts b/x-pack/plugins/observability_solution/observability/server/lib/rules/custom_threshold/register_custom_threshold_rule_type.ts
index 5a711455318a7..2fe8cbe76d294 100644
--- a/x-pack/plugins/observability_solution/observability/server/lib/rules/custom_threshold/register_custom_threshold_rule_type.ts
+++ b/x-pack/plugins/observability_solution/observability/server/lib/rules/custom_threshold/register_custom_threshold_rule_type.ts
@@ -36,7 +36,7 @@ import {
   valueActionVariableDescription,
   viewInAppUrlActionVariableDescription,
 } from './translations';
-import { oneOfLiterals } from './utils';
+import { oneOfLiterals, validateKQLStringFilter } from './utils';
 import {
   createCustomThresholdExecutor,
   CustomThresholdLocators,
@@ -57,11 +57,9 @@ export const searchConfigurationSchema = schema.object({
   index: schema.oneOf([schema.string(), dataViewSpecSchema]),
   query: schema.object({
     language: schema.string(),
-    query: schema.string(),
-    // TODO Enable KQL validation: https://github.com/elastic/kibana/issues/190029
-    // query: schema.string({
-    //   validate: validateKQLStringFilter,
-    // }),
+    query: schema.string({
+      validate: validateKQLStringFilter,
+    }),
   }),
   filter: schema.maybe(
     schema.arrayOf(
@@ -105,11 +103,9 @@ export function thresholdRuleType(
           name: schema.string(),
           aggType: schema.literal('count'),
           filter: schema.maybe(
-            schema.string()
-            // TODO Enable KQL validation: https://github.com/elastic/kibana/issues/190029
-            // schema.string({
-            //   validate: validateKQLStringFilter,
-            // })
+            schema.string({
+              validate: validateKQLStringFilter,
+            })
           ),
           field: schema.never(),
         }),
diff --git a/x-pack/plugins/observability_solution/observability/server/lib/rules/custom_threshold/utils.ts b/x-pack/plugins/observability_solution/observability/server/lib/rules/custom_threshold/utils.ts
index 783127978bae4..d79bdbb86d04f 100644
--- a/x-pack/plugins/observability_solution/observability/server/lib/rules/custom_threshold/utils.ts
+++ b/x-pack/plugins/observability_solution/observability/server/lib/rules/custom_threshold/utils.ts
@@ -52,7 +52,11 @@ export const validateKQLStringFilter = (value: string) => {
   }
 
   try {
-    kbnBuildEsQuery(undefined, [{ query: value, language: 'kuery' }], []);
+    kbnBuildEsQuery(undefined, [{ query: value, language: 'kuery' }], [], {
+      allowLeadingWildcards: true,
+      queryStringOptions: {},
+      ignoreFilterIfFieldNotInIndex: true,
+    });
   } catch (e) {
     return i18n.translate('xpack.observability.customThreshold.rule.schema.invalidFilterQuery', {
       defaultMessage: `filterQuery must be a valid KQL filter (error: ${e.message})`,