diff --git a/app/api/controller/pullreq/pr_find.go b/app/api/controller/pullreq/pr_find.go
index be885ccc1..cbd048e8b 100644
--- a/app/api/controller/pullreq/pr_find.go
+++ b/app/api/controller/pullreq/pr_find.go
@@ -58,3 +58,50 @@ func (c *Controller) Find(
 
 	return pr, nil
 }
+
+// Find returns a pull request from the provided repository.
+func (c *Controller) FindByBranches(
+	ctx context.Context,
+	session *auth.Session,
+	repoRef,
+	sourceRepoRef,
+	sourceBranch,
+	targetBranch string,
+) (*types.PullReq, error) {
+	if sourceBranch == "" || targetBranch == "" {
+		return nil, usererror.BadRequest("A valid source/target branch must be provided.")
+	}
+
+	targetRepo, err := c.getRepoCheckAccess(ctx, session, repoRef, enum.PermissionRepoView)
+	if err != nil {
+		return nil, fmt.Errorf("failed to acquire access to the repo: %w", err)
+	}
+
+	sourceRepo := targetRepo
+	if sourceRepoRef != repoRef {
+		sourceRepo, err = c.getRepoCheckAccess(ctx, session, sourceRepoRef, enum.PermissionRepoPush)
+		if err != nil {
+			return nil, fmt.Errorf("failed to acquire access to source repo: %w", err)
+		}
+	}
+
+	prs, err := c.pullreqStore.List(ctx, &types.PullReqFilter{
+		SourceRepoID: sourceRepo.ID,
+		SourceBranch: sourceBranch,
+		TargetRepoID: targetRepo.ID,
+		TargetBranch: targetBranch,
+		States:       []enum.PullReqState{enum.PullReqStateOpen},
+		Size:         1,
+		Sort:         enum.PullReqSortNumber,
+		Order:        enum.OrderAsc,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("failed to fetch existing pull request: %w", err)
+	}
+
+	if len(prs) == 0 {
+		return nil, usererror.ErrNotFound
+	}
+
+	return prs[0], nil
+}
diff --git a/app/api/handler/pullreq/pr_find.go b/app/api/handler/pullreq/pr_find.go
index 437443f75..84ac37163 100644
--- a/app/api/handler/pullreq/pr_find.go
+++ b/app/api/handler/pullreq/pr_find.go
@@ -49,3 +49,39 @@ func HandleFind(pullreqCtrl *pullreq.Controller) http.HandlerFunc {
 		render.JSON(w, http.StatusOK, pr)
 	}
 }
+
+// HandleFind returns a http.HandlerFunc that finds a pull request.
+func HandleFindByBranches(pullreqCtrl *pullreq.Controller) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		ctx := r.Context()
+		session, _ := request.AuthSessionFrom(ctx)
+
+		repoRef, err := request.GetRepoRefFromPath(r)
+		if err != nil {
+			render.TranslatedUserError(ctx, w, err)
+			return
+		}
+
+		sourceRepoRef := request.GetSourceRepoRefFromQueryOrDefault(r, repoRef)
+
+		sourceBranch, err := request.GetPullReqSourceBranchFromPath(r)
+		if err != nil {
+			render.TranslatedUserError(ctx, w, err)
+			return
+		}
+
+		targetBranch, err := request.GetPullReqTargetBranchFromPath(r)
+		if err != nil {
+			render.TranslatedUserError(ctx, w, err)
+			return
+		}
+
+		pr, err := pullreqCtrl.FindByBranches(ctx, session, repoRef, sourceRepoRef, sourceBranch, targetBranch)
+		if err != nil {
+			render.TranslatedUserError(ctx, w, err)
+			return
+		}
+
+		render.JSON(w, http.StatusOK, pr)
+	}
+}
diff --git a/app/api/openapi/pullreq.go b/app/api/openapi/pullreq.go
index 6d7ee5993..fe6d58b9d 100644
--- a/app/api/openapi/pullreq.go
+++ b/app/api/openapi/pullreq.go
@@ -47,6 +47,12 @@ type getPullReqRequest struct {
 	pullReqRequest
 }
 
+type getPullReqByBranchesRequest struct {
+	repoRequest
+	SourceBranch string `path:"source_branch"`
+	TargetBranch string `path:"target_branch"`
+}
+
 type updatePullReqRequest struct {
 	pullReqRequest
 	pullreq.UpdateInput
@@ -163,7 +169,7 @@ var queryParameterQueryPullRequest = openapi3.ParameterOrRef{
 
 var queryParameterSourceRepoRefPullRequest = openapi3.ParameterOrRef{
 	Parameter: &openapi3.Parameter{
-		Name:        "source_repo_ref",
+		Name:        request.QueryParamSourceRepoRef,
 		In:          openapi3.ParameterInQuery,
 		Description: ptr.String("Source repository ref of the pull requests."),
 		Required:    ptr.Bool(false),
@@ -518,6 +524,20 @@ func pullReqOperations(reflector *openapi3.Reflector) {
 	_ = reflector.SetJSONResponse(&getPullReq, new(usererror.Error), http.StatusForbidden)
 	_ = reflector.Spec.AddOperation(http.MethodGet, "/repos/{repo_ref}/pullreq/{pullreq_number}", getPullReq)
 
+	getPullReqByBranches := openapi3.Operation{}
+	getPullReqByBranches.WithTags("pullreq")
+	getPullReqByBranches.WithMapOfAnything(map[string]interface{}{"operationId": "getPullReqByBranches"})
+	getPullReqByBranches.WithParameters(queryParameterSourceRepoRefPullRequest)
+	_ = reflector.SetRequest(&getPullReqByBranches, new(getPullReqByBranchesRequest), http.MethodGet)
+	_ = reflector.SetJSONResponse(&getPullReqByBranches, new(types.PullReq), http.StatusOK)
+	_ = reflector.SetJSONResponse(&getPullReqByBranches, new(usererror.Error), http.StatusBadRequest)
+	_ = reflector.SetJSONResponse(&getPullReqByBranches, new(usererror.Error), http.StatusUnauthorized)
+	_ = reflector.SetJSONResponse(&getPullReqByBranches, new(usererror.Error), http.StatusForbidden)
+	_ = reflector.SetJSONResponse(&getPullReqByBranches, new(usererror.Error), http.StatusNotFound)
+	_ = reflector.SetJSONResponse(&getPullReqByBranches, new(usererror.Error), http.StatusInternalServerError)
+	_ = reflector.Spec.AddOperation(http.MethodGet,
+		"/repos/{repo_ref}/pullreq/{target_branch}...{source_branch}", getPullReqByBranches)
+
 	putPullReq := openapi3.Operation{}
 	putPullReq.WithTags("pullreq")
 	putPullReq.WithMapOfAnything(map[string]interface{}{"operationId": "updatePullReq"})
diff --git a/app/api/request/pullreq.go b/app/api/request/pullreq.go
index 9ed670d30..fd61fda1d 100644
--- a/app/api/request/pullreq.go
+++ b/app/api/request/pullreq.go
@@ -28,6 +28,8 @@ const (
 	PathParamPullReqCommentID = "pullreq_comment_id"
 	PathParamReviewerID       = "pullreq_reviewer_id"
 	PathParamUserGroupID      = "user_group_id"
+	PathParamSourceBranch     = "source_branch"
+	PathParamTargetBranch     = "target_branch"
 
 	QueryParamAuthorID           = "author_id"
 	QueryParamCommenterID        = "commenter_id"
@@ -35,6 +37,7 @@ const (
 	QueryParamReviewDecision     = "review_decision"
 	QueryParamMentionedID        = "mentioned_id"
 	QueryParamExcludeDescription = "exclude_description"
+	QueryParamSourceRepoRef      = "source_repo_ref"
 )
 
 func GetPullReqNumberFromPath(r *http.Request) (int64, error) {
@@ -52,6 +55,18 @@ func GetPullReqCommentIDPath(r *http.Request) (int64, error) {
 	return PathParamAsPositiveInt64(r, PathParamPullReqCommentID)
 }
 
+func GetPullReqSourceBranchFromPath(r *http.Request) (string, error) {
+	return PathParamOrError(r, PathParamSourceBranch)
+}
+
+func GetPullReqTargetBranchFromPath(r *http.Request) (string, error) {
+	return PathParamOrError(r, PathParamTargetBranch)
+}
+
+func GetSourceRepoRefFromQueryOrDefault(r *http.Request, deflt string) string {
+	return QueryParamOrDefault(r, QueryParamSourceRepoRef, deflt)
+}
+
 // ParseSortPullReq extracts the pull request sort parameter from the url.
 func ParseSortPullReq(r *http.Request) enum.PullReqSort {
 	result, _ := enum.PullReqSort(r.URL.Query().Get(QueryParamSort)).Sanitize()
diff --git a/app/router/api.go b/app/router/api.go
index fa7779d44..41bf3b247 100644
--- a/app/router/api.go
+++ b/app/router/api.go
@@ -638,6 +638,10 @@ func SetupPullReq(r chi.Router, pullreqCtrl *pullreq.Controller) {
 	r.Route("/pullreq", func(r chi.Router) {
 		r.Post("/", handlerpullreq.HandleCreate(pullreqCtrl))
 		r.Get("/", handlerpullreq.HandleList(pullreqCtrl))
+		r.Get(
+			fmt.Sprintf("/{%s}...{%s}", request.PathParamTargetBranch, request.PathParamSourceBranch),
+			handlerpullreq.HandleFindByBranches(pullreqCtrl),
+		)
 
 		r.Route(fmt.Sprintf("/{%s}", request.PathParamPullReqNumber), func(r chi.Router) {
 			r.Get("/", handlerpullreq.HandleFind(pullreqCtrl))