diff --git a/reactivex/observable/observable.py b/reactivex/observable/observable.py
index 6e864da9..e540fe46 100644
--- a/reactivex/observable/observable.py
+++ b/reactivex/observable/observable.py
@@ -229,7 +229,7 @@ def pipe(self, *operators: Callable[[Any], Any]) -> Any:
 
         return pipe_(self, *operators)
 
-    def run(self) -> Any:
+    def run(self, scheduler: Optional[abc.SchedulerBase] = None) -> _T_out:
         """Run source synchronously.
 
         Subscribes to the observable source. Then blocks and waits for the
@@ -249,7 +249,7 @@ def run(self) -> Any:
         """
         from ..run import run
 
-        return run(self)
+        return run(self, scheduler)
 
     def __await__(self) -> Generator[Any, None, _T_out]:
         """Awaits the given observable.
diff --git a/reactivex/run.py b/reactivex/run.py
index 6e932b2e..15b1950b 100644
--- a/reactivex/run.py
+++ b/reactivex/run.py
@@ -1,17 +1,18 @@
 import threading
 from typing import Optional, TypeVar, cast
 
+from reactivex import abc
 from reactivex.internal.exceptions import SequenceContainsNoElementsError
 from reactivex.scheduler import NewThreadScheduler
 
 from .observable import Observable
 
-scheduler = NewThreadScheduler()
+_default_scheduler = NewThreadScheduler()
 
 _T = TypeVar("_T")
 
 
-def run(source: Observable[_T]) -> _T:
+def run(source: Observable[_T], scheduler: Optional[abc.SchedulerBase] = None) -> _T:
     """Run source synchronously.
 
     Subscribes to the observable source. Then blocks and waits for the
@@ -32,6 +33,7 @@ def run(source: Observable[_T]) -> _T:
     Returns:
         The last element emitted from the observable.
     """
+    scheduler = scheduler or _default_scheduler
     exception: Optional[Exception] = None
     latch = threading.Event()
     has_result = False