diff --git a/sdks/python/apache_beam/runners/direct/evaluation_context.py b/sdks/python/apache_beam/runners/direct/evaluation_context.py
index d10c57baa43a..2b22c086099b 100644
--- a/sdks/python/apache_beam/runners/direct/evaluation_context.py
+++ b/sdks/python/apache_beam/runners/direct/evaluation_context.py
@@ -43,6 +43,7 @@
   from apache_beam.runners.direct.bundle_factory import BundleFactory, _Bundle
   from apache_beam.utils.timestamp import Timestamp
 
+
 class _ExecutionContext(object):
   """Contains the context for the execution of a single PTransform.
 
@@ -389,6 +390,7 @@ def extract_all_timers(self):
     return self._watermark_manager.extract_all_timers()
 
   def is_done(self, transform=None):
+    # type: (Optional[AppliedPTransform]) -> bool
     """Checks completion of a step or the pipeline.
 
     Args:
@@ -407,6 +409,7 @@ def is_done(self, transform=None):
     return True
 
   def _is_transform_done(self, transform):
+    # type: (AppliedPTransform) -> bool
     tw = self._watermark_manager.get_watermarks(transform)
     return tw.output_watermark == WatermarkManager.WATERMARK_POS_INF
 
diff --git a/sdks/python/apache_beam/runners/direct/executor.py b/sdks/python/apache_beam/runners/direct/executor.py
index 32a6b32ea561..a49e2e992c4a 100644
--- a/sdks/python/apache_beam/runners/direct/executor.py
+++ b/sdks/python/apache_beam/runners/direct/executor.py
@@ -25,9 +25,13 @@
 import sys
 import threading
 import traceback
+import typing
 from builtins import object
 from builtins import range
 from weakref import WeakValueDictionary
+from typing import Generic
+from typing import Type
+from typing import TypeVar
 
 from future.moves import queue
 from future.utils import raise_
@@ -37,6 +41,11 @@
 from apache_beam.transforms import sideinputs
 from apache_beam.utils import counters
 
+if typing.TYPE_CHECKING:
+  from apache_beam.runners.direct.evaluation_context import EvaluationContext
+
+T = TypeVar('T')
+
 
 class _ExecutorService(object):
   """Thread pool for executing tasks in parallel."""
@@ -408,8 +417,11 @@ class _ExecutorServiceParallelExecutor(object):
 
   NUM_WORKERS = 1
 
-  def __init__(self, value_to_consumers, transform_evaluator_registry,
-               evaluation_context):
+  def __init__(self,
+               value_to_consumers,
+               transform_evaluator_registry,
+               evaluation_context  # type: EvaluationContext
+              ):
     self.executor_service = _ExecutorService(
         _ExecutorServiceParallelExecutor.NUM_WORKERS)
     self.transform_executor_services = _TransformExecutorServices(
@@ -481,14 +493,16 @@ def schedule_consumption(self, consumer_applied_ptransform, committed_bundle,
         on_complete, transform_executor_service)
     transform_executor_service.schedule(transform_executor)
 
-  class _TypedUpdateQueue(object):
+  class _TypedUpdateQueue(Generic[T]):
     """Type checking update queue with blocking and non-blocking operations."""
 
     def __init__(self, item_type):
+      # type: (Type[T]) -> None
       self._item_type = item_type
-      self._queue = queue.Queue()
+      self._queue = queue.Queue()  # type: queue.Queue[T]
 
     def poll(self):
+      # type: () -> Optional[T]
       try:
         item = self._queue.get_nowait()
         self._queue.task_done()
@@ -497,6 +511,7 @@ def poll(self):
         return None
 
     def take(self):
+      # type: () -> T
       # The implementation of Queue.Queue.get() does not propagate
       # KeyboardInterrupts when a timeout is not used.  We therefore use a
       # one-second timeout in the following loop to allow KeyboardInterrupts
@@ -510,6 +525,7 @@ def take(self):
           pass
 
     def offer(self, item):
+      # type: (T) -> None
       assert isinstance(item, self._item_type)
       self._queue.put_nowait(item)
 
@@ -548,6 +564,7 @@ class _MonitorTask(_ExecutorService.CallableTask):
     """MonitorTask continuously runs to ensure that pipeline makes progress."""
 
     def __init__(self, executor):
+      # type: (_ExecutorServiceParallelExecutor) -> None
       self._executor = executor
 
     @property
diff --git a/sdks/python/apache_beam/runners/direct/watermark_manager.py b/sdks/python/apache_beam/runners/direct/watermark_manager.py
index 23431f16ddbc..5a0c4179542a 100644
--- a/sdks/python/apache_beam/runners/direct/watermark_manager.py
+++ b/sdks/python/apache_beam/runners/direct/watermark_manager.py
@@ -20,7 +20,9 @@
 from __future__ import absolute_import
 
 import threading
+import typing
 from builtins import object
+from typing import Dict
 
 from apache_beam import pipeline
 from apache_beam import pvalue
@@ -29,6 +31,9 @@
 from apache_beam.utils.timestamp import MIN_TIMESTAMP
 from apache_beam.utils.timestamp import TIME_GRANULARITY
 
+if typing.TYPE_CHECKING:
+  from apache_beam.pipeline import AppliedPTransform
+
 
 class WatermarkManager(object):
   """For internal use only; no backwards-compatibility guarantees.
@@ -45,7 +50,7 @@ def __init__(self, clock, root_transforms, value_to_consumers,
     self._value_to_consumers = value_to_consumers
     self._transform_keyed_states = transform_keyed_states
     # AppliedPTransform -> TransformWatermarks
-    self._transform_to_watermarks = {}
+    self._transform_to_watermarks = {}  # type: Dict[AppliedPTransform, _TransformWatermarks]
 
     for root_transform in root_transforms:
       self._transform_to_watermarks[root_transform] = _TransformWatermarks(
@@ -73,6 +78,7 @@ def _update_input_transform_watermarks(self, applied_ptransform):
             input_transform_watermarks)
 
   def get_watermarks(self, applied_ptransform):
+    # type: (AppliedPTransform) -> _TransformWatermarks
     """Gets the input and output watermarks for an AppliedPTransform.
 
     If the applied_ptransform has not processed any elements, return a