diff --git a/.github/workflows/test-acceptance.yaml b/.github/workflows/test-acceptance.yaml
index ddc65f39b1..7b879b4acf 100644
--- a/.github/workflows/test-acceptance.yaml
+++ b/.github/workflows/test-acceptance.yaml
@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false  # continue other tests if one test in matrix fails
       matrix:
-        node-version: [18.x]
+        node-version: [20.x]
         os: [macos-latest, windows-latest, ubuntu-latest]
         type: [smoke, plugins, styles, dev, prod, errors]
 
diff --git a/.github/workflows/test-heroku.yaml b/.github/workflows/test-heroku.yaml
index cbfbd27171..1b15ea5544 100644
--- a/.github/workflows/test-heroku.yaml
+++ b/.github/workflows/test-heroku.yaml
@@ -22,7 +22,7 @@ jobs:
       uses: actions/setup-node@v3
       with:
         cache: 'npm'
-        node-version: '18'
+        node-version: '20'
     - name: Cache Cypress binary
       uses: actions/cache@v3
       with:
diff --git a/.github/workflows/test.yaml b/.github/workflows/test.yaml
index fe8433fdaa..eb611e3151 100644
--- a/.github/workflows/test.yaml
+++ b/.github/workflows/test.yaml
@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false  # continue other tests if one test in matrix fails
       matrix:
-        node-version: [16.x, 18.x]
+        node-version: [16.x, 18.x, 20.x]
         os: [macos-latest, windows-latest, ubuntu-latest]
 
     name: Test kit on Node v${{ matrix.node-version }} (${{ matrix.os }})
diff --git a/.nvmrc b/.nvmrc
index b009dfb9d9..9de2256827 100644
--- a/.nvmrc
+++ b/.nvmrc
@@ -1 +1 @@
-lts/*
+lts/iron
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 68647c8251..36cebc0ed1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+### New features
+
+- [#2363: Support for the new Node LTS (version 20)](https://github.com/alphagov/govuk-prototype-kit/pull/2363)
+
 ## 13.13.6
 
 ### Fixes
diff --git a/bin/cli b/bin/cli
index 27f9f73c3d..bafa217d0f 100755
--- a/bin/cli
+++ b/bin/cli
@@ -2,16 +2,16 @@
 
 if (process.argv.indexOf('--suppress-node-version-warning') === -1 || (process.argv[2] === 'migrate' && process.argv[3] === '--')) {
   const majorNodeVersion = parseInt(process.version.split('.')[0].substring(1), 10)
-  const versionIsWithinRecommendation = majorNodeVersion === 18 || majorNodeVersion === 16
+  const versionIsWithinRecommendation = [16, 18, 20].includes(majorNodeVersion)
   if (!versionIsWithinRecommendation) {
     const nodeVersionIsTooOldToUse = majorNodeVersion < 14
-    const updateOrDownload = majorNodeVersion < 18 ? 'update to' : 'download'
+    const updateOrDownload = majorNodeVersion < 20 ? 'update to' : 'download'
     const printLn = nodeVersionIsTooOldToUse ? console.error.bind(console) : console.warn.bind(console)
     const additionalText = nodeVersionIsTooOldToUse ? '' : ' Some features may not work with your version.'
 
     printLn('\nYou\'re using Node', process.version)
-    printLn('The GOV.UK Prototype Kit only supports Node v16 and v18.' + additionalText + '\n')
-    printLn('You can', updateOrDownload, 'Node v18 at https://nodejs.org/en/download\n')
+    printLn('The GOV.UK Prototype Kit only supports Node v16, v18 and v20.' + additionalText + '\n')
+    printLn('You can', updateOrDownload, 'Node v20 at https://nodejs.org/en/download\n')
 
     if (nodeVersionIsTooOldToUse) {
       process.exit(0)
diff --git a/lib/plugins/plugin-validator.spec.js b/lib/plugins/plugin-validator.spec.js
index 50dbf5a1ea..e98cca58f4 100644
--- a/lib/plugins/plugin-validator.spec.js
+++ b/lib/plugins/plugin-validator.spec.js
@@ -13,12 +13,23 @@ describe('plugin-validator', () => {
   const validSuccessMessages = phaseOneSuccessMessages.concat([ansiColors.green('The plugin config is valid.')])
 
   beforeEach(() => {
+    // Polyfill process.exitCode property for Node.js < v20
+    const originalExitCode = process.exitCode
+    if (!process.exitCode) {
+      Object.defineProperty(process, 'exitCode', {
+        get: jest.fn(),
+        set: jest.fn()
+      })
+    }
     const mockFileSystemRoot = path.join(process.cwd(), 'example-plugin')
+    const exitCodeSetterSpy = jest.spyOn(process, 'exitCode', 'set').mockImplementation(() => {})
     testScope = {
       mockFileSystemRoot,
       fileSystem: mockFileSystem(mockFileSystemRoot),
       stdLogs: [],
-      errLogs: []
+      errLogs: [],
+      exitCodeSetterSpy,
+      originalExitCode
     }
     jest.spyOn(console, 'log').mockImplementation((message, ...args) => {
       if (args.length > 0) {
@@ -40,6 +51,8 @@ describe('plugin-validator', () => {
 
   afterEach(() => {
     jest.clearAllMocks()
+    // Reset polyfill process.exitCode property for Node.js < v20
+    process.exitCode = testScope.originalExitCode
   })
 
   describe('unexpected keys', () => {
@@ -50,6 +63,7 @@ describe('plugin-validator', () => {
       await validatePlugin(testScope.mockFileSystemRoot)
       expect(testScope.errLogs).toEqual([ansiColors.red('Error: The following invalid keys exist in your config: myExample')])
       expect(testScope.stdLogs).toEqual(phaseOneSuccessMessages)
+      expect(testScope.exitCodeSetterSpy).toHaveBeenCalledWith(100)
     })
     it('should allow a single unknown key when specified', async () => {
       testScope.fileSystem.writeFile(['govuk-prototype-kit.config.json'], JSON.stringify({
diff --git a/npm-shrinkwrap.json b/npm-shrinkwrap.json
index 0927544a30..deea975653 100644
--- a/npm-shrinkwrap.json
+++ b/npm-shrinkwrap.json
@@ -56,7 +56,7 @@
         "wait-on": "^7.0.1"
       },
       "engines": {
-        "node": "^16.x || >= 18.x"
+        "node": "^18.x || >= 20.x"
       }
     },
     "node_modules/@aashutoshrathi/word-wrap": {
diff --git a/package.json b/package.json
index 6ab539bedc..fa9583c557 100644
--- a/package.json
+++ b/package.json
@@ -3,7 +3,7 @@
   "description": "Rapidly create HTML prototypes of GOV.UK services",
   "version": "13.13.6",
   "engines": {
-    "node": "^16.x || >= 18.x"
+    "node": "^16.x || ^18.x || >= 20.x"
   },
   "main": "index.js",
   "bin": {