diff --git a/readthedocs/api/v2/views/integrations.py b/readthedocs/api/v2/views/integrations.py
index 4424238a78b..1567e71b18e 100644
--- a/readthedocs/api/v2/views/integrations.py
+++ b/readthedocs/api/v2/views/integrations.py
@@ -19,7 +19,11 @@
     webhook_github,
     webhook_gitlab,
 )
-from readthedocs.core.views.hooks import build_branches, sync_versions
+from readthedocs.core.views.hooks import (
+    build_branches,
+    sync_versions,
+    get_or_create_external_version,
+)
 from readthedocs.integrations.models import HttpExchange, Integration
 from readthedocs.projects.models import Project
 
@@ -29,6 +33,9 @@
 GITHUB_EVENT_HEADER = 'HTTP_X_GITHUB_EVENT'
 GITHUB_SIGNATURE_HEADER = 'HTTP_X_HUB_SIGNATURE'
 GITHUB_PUSH = 'push'
+GITHUB_PULL_REQUEST = 'pull_request'
+GITHUB_PULL_REQUEST_OPEN = 'opened'
+GITHUB_PULL_REQUEST_SYNC = 'synchronize'
 GITHUB_CREATE = 'create'
 GITHUB_DELETE = 'delete'
 GITLAB_TOKEN_HEADER = 'HTTP_X_GITLAB_TOKEN'
@@ -110,6 +117,10 @@ def handle_webhook(self):
         """Handle webhook payload."""
         raise NotImplementedError
 
+    def get_external_version_data(self):
+        """Get External Version data from payload."""
+        raise NotImplementedError
+
     def is_payload_valid(self):
         """Validates the webhook's payload using the integration's secret."""
         return False
@@ -218,6 +229,13 @@ def get_data(self):
                 pass
         return super().get_data()
 
+    def get_external_version_data(self):
+        """Get Commit Sha and pull request number from payload"""
+        identifier = self.data['pull_request']['head']['sha']
+        verbose_name = str(self.data['number'])
+
+        return identifier, verbose_name
+
     def is_payload_valid(self):
         """
         GitHub use a HMAC hexdigest hash to sign the payload.
@@ -271,6 +289,21 @@ def handle_webhook(self):
                 raise ParseError('Parameter "ref" is required')
         if event in (GITHUB_CREATE, GITHUB_DELETE):
             return self.sync_versions(self.project)
+
+        if (
+            event == GITHUB_PULL_REQUEST and
+            self.data['action'] in [GITHUB_PULL_REQUEST_OPEN, GITHUB_PULL_REQUEST_SYNC]
+        ):
+            try:
+                identifier, verbose_name = self.get_external_version_data()
+                external_version = get_or_create_external_version(
+                    self.project, identifier, verbose_name
+                )
+                return self.get_response_push(self.project, [external_version.verbose_name])
+
+            except KeyError:
+                raise ParseError('Parameters "sha" and "number" are required')
+
         return None
 
     def _normalize_ref(self, ref):
diff --git a/readthedocs/core/views/hooks.py b/readthedocs/core/views/hooks.py
index a3273a88871..bd5b8c40cb0 100644
--- a/readthedocs/core/views/hooks.py
+++ b/readthedocs/core/views/hooks.py
@@ -2,6 +2,8 @@
 
 import logging
 
+from readthedocs.builds.constants import EXTERNAL
+from readthedocs.builds.models import Version
 from readthedocs.core.utils import trigger_build
 from readthedocs.projects.tasks import sync_repository_task
 
@@ -88,3 +90,21 @@ def sync_versions(project):
     except Exception:
         log.exception('Unknown sync versions exception')
     return None
+
+
+def get_or_create_external_version(project, identifier, verbose_name):
+    external_version = project.versions(manager=EXTERNAL).filter(verbose_name=verbose_name).first()
+    if external_version:
+        if external_version.identifier != identifier:
+            external_version.identifier = identifier
+            external_version.save()
+    else:
+        created_external_version = Version.objects.create(
+            project=project,
+            type=EXTERNAL,
+            identifier=identifier,
+            verbose_name=verbose_name,
+            active=True
+        )
+        return created_external_version
+    return external_version
diff --git a/readthedocs/projects/constants.py b/readthedocs/projects/constants.py
index 7c83cffd7ea..8b770830f79 100644
--- a/readthedocs/projects/constants.py
+++ b/readthedocs/projects/constants.py
@@ -333,3 +333,5 @@
     'https://gitlab.com/{user}/{repo}/'
     '{action}/{version}{docroot}{path}{source_suffix}'
 )
+
+GITHUB_GIT_PATTERN = 'pull/{id}/head:external-{id}'
diff --git a/readthedocs/projects/tasks.py b/readthedocs/projects/tasks.py
index 7efcd5a762a..2d0e087b2a2 100644
--- a/readthedocs/projects/tasks.py
+++ b/readthedocs/projects/tasks.py
@@ -138,7 +138,7 @@ def sync_repo(self):
                 }
             )
             version_repo = self.get_vcs_repo()
-            version_repo.update()
+            version_repo.update(version=self.version)
             self.sync_versions(version_repo)
             version_repo.checkout(self.version.identifier)
         finally:
diff --git a/readthedocs/vcs_support/backends/bzr.py b/readthedocs/vcs_support/backends/bzr.py
index e228ac720d3..99029d6dc82 100644
--- a/readthedocs/vcs_support/backends/bzr.py
+++ b/readthedocs/vcs_support/backends/bzr.py
@@ -17,7 +17,7 @@ class Backend(BaseVCS):
     supports_tags = True
     fallback_branch = ''
 
-    def update(self):
+    def update(self, version=None):  # pylint: disable=arguments-differ
         super().update()
         retcode = self.run('bzr', 'status', record=False)[0]
         if retcode == 0:
diff --git a/readthedocs/vcs_support/backends/git.py b/readthedocs/vcs_support/backends/git.py
index aa3adc6c2bc..506143132ed 100644
--- a/readthedocs/vcs_support/backends/git.py
+++ b/readthedocs/vcs_support/backends/git.py
@@ -10,7 +10,9 @@
 from django.core.exceptions import ValidationError
 from git.exc import BadName, InvalidGitRepositoryError
 
+from readthedocs.builds.constants import EXTERNAL
 from readthedocs.config import ALL
+from readthedocs.projects.constants import GITHUB_GIT_PATTERN
 from readthedocs.projects.exceptions import RepositoryError
 from readthedocs.projects.validators import validate_submodule_url
 from readthedocs.vcs_support.base import BaseVCS, VCSVersion
@@ -25,6 +27,7 @@ class Backend(BaseVCS):
 
     supports_tags = True
     supports_branches = True
+    supports_external_branches = True
     supports_submodules = True
     fallback_branch = 'master'  # default branch
     repo_depth = 50
@@ -50,13 +53,20 @@ def _get_clone_url(self):
     def set_remote_url(self, url):
         return self.run('git', 'remote', 'set-url', 'origin', url)
 
-    def update(self):
+    def update(self, version=None):  # pylint: disable=arguments-differ
         """Clone or update the repository."""
         super().update()
         if self.repo_exists():
             self.set_remote_url(self.repo_url)
+            # A fetch is always required to get external versions properly
+            if version and version.type == EXTERNAL:
+                return self.fetch(version.verbose_name)
             return self.fetch()
         self.make_clean_working_dir()
+        # A fetch is always required to get external versions properly
+        if version and version.type == EXTERNAL:
+            self.clone()
+            return self.fetch(version.verbose_name)
         return self.clone()
 
     def repo_exists(self):
@@ -143,8 +153,14 @@ def use_shallow_clone(self):
         from readthedocs.projects.models import Feature
         return not self.project.has_feature(Feature.DONT_SHALLOW_CLONE)
 
-    def fetch(self):
-        cmd = ['git', 'fetch', '--tags', '--prune', '--prune-tags']
+    def fetch(self, verbose_name=None):
+        cmd = ['git', 'fetch', 'origin',
+               '--tags', '--prune', '--prune-tags']
+
+        if verbose_name and 'github.com' in self.repo_url:
+            cmd.append(
+                GITHUB_GIT_PATTERN.format(id=verbose_name)
+            )
 
         if self.use_shallow_clone():
             cmd.extend(['--depth', str(self.repo_depth)])
diff --git a/readthedocs/vcs_support/backends/hg.py b/readthedocs/vcs_support/backends/hg.py
index 0361bfa462c..9b44faeed2e 100644
--- a/readthedocs/vcs_support/backends/hg.py
+++ b/readthedocs/vcs_support/backends/hg.py
@@ -13,7 +13,7 @@ class Backend(BaseVCS):
     supports_branches = True
     fallback_branch = 'default'
 
-    def update(self):
+    def update(self, version=None):  # pylint: disable=arguments-differ
         super().update()
         retcode = self.run('hg', 'status', record=False)[0]
         if retcode == 0:
diff --git a/readthedocs/vcs_support/backends/svn.py b/readthedocs/vcs_support/backends/svn.py
index b1a945aec2c..50bab45a512 100644
--- a/readthedocs/vcs_support/backends/svn.py
+++ b/readthedocs/vcs_support/backends/svn.py
@@ -27,7 +27,7 @@ def __init__(self, *args, **kwargs):
         else:
             self.base_url = self.repo_url
 
-    def update(self):
+    def update(self, version=None):  # pylint: disable=arguments-differ
         super().update()
         # For some reason `svn status` gives me retcode 0 in non-svn
         # directories that's why I use `svn info` here.