diff --git a/anymail/backends/sendgrid.py b/anymail/backends/sendgrid.py
index b7e6f44..8434735 100644
--- a/anymail/backends/sendgrid.py
+++ b/anymail/backends/sendgrid.py
@@ -290,6 +290,12 @@ class SendGridPayload(RequestsPayload):
     def set_template_id(self, template_id):
         self.add_filter('templates', 'enable', 1)
         self.add_filter('templates', 'template_id', template_id)
+        # Must ensure text and html are non-empty, or template parts won't render.
+        # https://sendgrid.com/docs/API_Reference/Web_API_v3/Transactional_Templates/smtpapi.html#-Text-or-HTML-Templates
+        if not self.data.get("text", ""):
+            self.data["text"] = " "
+        if not self.data.get("html", ""):
+            self.data["html"] = " "
 
     def set_merge_data(self, merge_data):
         # Becomes smtpapi['sub'] in build_merge_data, after we know recipients and merge_field_format.
diff --git a/docs/esps/sendgrid.rst b/docs/esps/sendgrid.rst
index be169f0..6cc9dbf 100644
--- a/docs/esps/sendgrid.rst
+++ b/docs/esps/sendgrid.rst
@@ -282,6 +282,11 @@ your SendGrid template definition where you want the message-specific versions
 to appear). If you don't want to supply any additional subject or body content
 from your Django app, set those EmailMessage attributes to empty strings.
 
+(Anymail will convert empty text and HTML bodies to single spaces whenever
+:attr:`~anymail.message.AnymailMessage.template_id` is set, to ensure the
+plaintext and HTML from your template are present in your outgoing email.
+This works around a `limitation in SendGrid's template rendering`_.)
+
 See the `SendGrid's template overview`_ and `transactional template docs`_
 for more information.
 
@@ -289,6 +294,8 @@ for more information.
     https://sendgrid.com/docs/User_Guide/Transactional_Templates/index.html
 .. _transactional template docs:
     https://sendgrid.com/docs/API_Reference/Web_API_v3/Transactional_Templates/smtpapi.html
+.. _limitation in SendGrid's template rendering:
+    https://sendgrid.com/docs/API_Reference/Web_API_v3/Transactional_Templates/smtpapi.html#-Text-or-HTML-Templates
 
 
 .. _sendgrid-webhooks:
diff --git a/tests/test_sendgrid_backend.py b/tests/test_sendgrid_backend.py
index 42ffa89..f0b764d 100644
--- a/tests/test_sendgrid_backend.py
+++ b/tests/test_sendgrid_backend.py
@@ -400,6 +400,7 @@ class SendGridBackendAnymailFeatureTests(SendGridBackendMockAPITestCase):
         self.assertEqual(smtpapi['filters']['opentrack'], {'settings': {'enable': 0}})
 
     def test_template_id(self):
+        self.message.attach_alternative("HTML Body", "text/html")
         self.message.template_id = "5997fcf6-2b9f-484d-acd5-7e9a99f0dc1f"
         self.message.send()
         smtpapi = self.get_smtpapi()
@@ -407,6 +408,19 @@ class SendGridBackendAnymailFeatureTests(SendGridBackendMockAPITestCase):
             'settings': {'enable': 1,
                          'template_id': "5997fcf6-2b9f-484d-acd5-7e9a99f0dc1f"}
         })
+        data = self.get_api_call_data()
+        self.assertEqual(data['text'], "Text Body")
+        self.assertEqual(data['html'], "HTML Body")
+
+    def test_template_id_with_empty_body(self):
+        # Text and html must be present (and non-empty-string), or the corresponding
+        # part will not render from the template. Make sure we fill in strings:
+        message = mail.EmailMessage(from_email='from@example.com', to=['to@example.com'])
+        message.template_id = "5997fcf6-2b9f-484d-acd5-7e9a99f0dc1f"
+        message.send()
+        data = self.get_api_call_data()
+        self.assertEqual(data['text'], " ")  # single space is sufficient
+        self.assertEqual(data['html'], " ")
 
     def test_merge_data(self):
         self.message.from_email = 'from@example.com'