diff --git a/.github/scripts/assign_backport_reviewer.js b/.github/scripts/assign_backport_reviewer.js
new file mode 100644
index 0000000000000..4c5add0253f00
--- /dev/null
+++ b/.github/scripts/assign_backport_reviewer.js
@@ -0,0 +1,172 @@
+const normalize = (value) => value.replace(/^@/, '').trim();
+
+const isHumanReviewer = (login) =>
+  Boolean(login) && login !== 'kibanamachine' && !login.endsWith('[bot]');
+
+const getOriginalPrNumber = ({ title, body }) => {
+  const sourcePullRequestIndex = body.indexOf('"sourcePullRequest"');
+  const originalPrNumberFromMetadata =
+    sourcePullRequestIndex === -1
+      ? undefined
+      : body
+          .slice(sourcePullRequestIndex)
+          .match(/"number"\s*:\s*(\d+)/)?.[1];
+  const originalPrNumberFromTitle = title.match(/\(#(\d+)\)\s*$/)?.[1];
+
+  return Number(originalPrNumberFromMetadata ?? originalPrNumberFromTitle);
+};
+
+const getReviews = async ({ github, owner, repo, originalPrNumber }) => {
+  const reviewHistory = await github.graphql(
+    `query($owner: String!, $repo: String!, $number: Int!) {
+      repository(owner: $owner, name: $repo) {
+        pullRequest(number: $number) {
+          reviews(first: 100) {
+            nodes {
+              state
+              submittedAt
+              author {
+                login
+              }
+              onBehalfOf(first: 10) {
+                nodes {
+                  slug
+                  organization {
+                    login
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+    }`,
+    {
+      owner,
+      repo,
+      number: originalPrNumber,
+    }
+  );
+
+  return (reviewHistory.repository.pullRequest?.reviews?.nodes ?? [])
+    .filter((review) => Boolean(review.submittedAt))
+    .sort((a, b) => Date.parse(b.submittedAt) - Date.parse(a.submittedAt));
+};
+
+const getReviewedTeams = (reviews) => {
+  const reviewedTeams = [];
+
+  for (const review of reviews) {
+    for (const team of review.onBehalfOf.nodes ?? []) {
+      const combinedSlug = `${team.organization.login}/${team.slug}`;
+      if (!reviewedTeams.includes(combinedSlug)) {
+        reviewedTeams.push(combinedSlug);
+      }
+    }
+  }
+
+  return reviewedTeams;
+};
+
+const getMatchedTeams = async ({ github, core, prAuthor, reviewedTeams }) => {
+  try {
+    const result = await github.graphql(
+      `query($login: String!) {
+        organization(login: "elastic") {
+          teams(first: 100, userLogins: [$login]) {
+            nodes { combinedSlug }
+          }
+        }
+      }`,
+      { login: prAuthor }
+    );
+    const authorTeams = new Set(
+      result.organization.teams.nodes.map((team) => normalize(team.combinedSlug))
+    );
+
+    return reviewedTeams.filter((team) => authorTeams.has(team));
+  } catch (error) {
+    core.warning(`Failed to query author's org teams: ${error.message}`);
+    return [];
+  }
+};
+
+const getFallbackReviewer = ({ reviews, prAuthor }) => {
+  const fallbackReview = reviews.find((review) => {
+    const login = review.author?.login;
+
+    return (
+      review.state === 'APPROVED' &&
+      isHumanReviewer(login) &&
+      login !== prAuthor &&
+      Boolean(review.submittedAt)
+    );
+  });
+
+  return fallbackReview?.author.login;
+};
+
+const requestReviewers = async ({ github, pullRequestId, teamReviewers, reviewer }) => {
+  await github.graphql(
+    `mutation RequestReviewsByLogin(
+      $pullRequestId: ID!
+      $userLogins: [String!]
+      $teamSlugs: [String!]
+    ) {
+      requestReviewsByLogin(
+        input: {
+          pullRequestId: $pullRequestId
+          userLogins: $userLogins
+          teamSlugs: $teamSlugs
+          union: false
+        }
+      ) {
+        clientMutationId
+      }
+    }`,
+    {
+      pullRequestId,
+      userLogins: reviewer ? [reviewer] : [],
+      teamSlugs: teamReviewers,
+    }
+  );
+};
+
+module.exports = async ({ github, context, core }) => {
+  const { owner, repo } = context.repo;
+  const pullRequest = context.payload.pull_request;
+  const prAuthor = pullRequest.user.login;
+  const title = pullRequest.title ?? '';
+  const body = pullRequest.body ?? '';
+  const originalPrNumber = getOriginalPrNumber({ title, body });
+
+  if (!Number.isInteger(originalPrNumber)) {
+    core.info('No source pull request number found');
+    return;
+  }
+
+  const reviews = await getReviews({ github, owner, repo, originalPrNumber });
+  const reviewedTeams = getReviewedTeams(reviews);
+  const teamReviewers = await getMatchedTeams({
+    github,
+    core,
+    prAuthor,
+    reviewedTeams,
+  });
+  const reviewer =
+    teamReviewers.length > 0 ? undefined : getFallbackReviewer({ reviews, prAuthor });
+
+  if (teamReviewers.length === 0 && !reviewer) {
+    core.info('No team reviewers or fallback reviewer found');
+    return;
+  }
+
+  core.info(`Updating reviewers: teamReviewers=${teamReviewers}, reviewer=${reviewer}`);
+
+  await requestReviewers({
+    github,
+    pullRequestId: pullRequest.node_id,
+    teamReviewers,
+    reviewer,
+  });
+};
diff --git a/.github/workflows/assign-backport-reviewer.yml b/.github/workflows/assign-backport-reviewer.yml
new file mode 100644
index 0000000000000..8d5f9c6acfd40
--- /dev/null
+++ b/.github/workflows/assign-backport-reviewer.yml
@@ -0,0 +1,34 @@
+name: Assign manual backport reviewer
+
+on:
+  pull_request_target:
+    branches:
+      - '8.19'
+      - '9.*'
+      - '[1-9][0-9]*.*'
+    types:
+      - opened
+
+jobs:
+  assign-reviewer:
+    name: Find reviewer for manual backport
+    runs-on: ubuntu-latest
+    if: |
+      github.event.pull_request.user.login != 'kibanamachine' &&
+      contains(github.event.pull_request.labels.*.name, 'backport')
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+          sparse-checkout: .github
+          sparse-checkout-cone-mode: true
+          fetch-depth: 1
+
+      - name: Assign reviewers
+        uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd # v8.0.0
+        with:
+          github-token: ${{ secrets.KIBANAMACHINE_TOKEN }}
+          script: |
+            const assignBackportReviewer = require('./.github/scripts/assign_backport_reviewer');
+            await assignBackportReviewer({ github, context, core });