diff --git a/CHANGELOG.md b/CHANGELOG.md
index 34eaf6e359257..9330b1e7fdfae 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -264,6 +264,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Deprecated the use of `CheckpointConnector.hpc_load()` in favor of `CheckpointConnector.restore()` ([#7652](https://github.com/PyTorchLightning/pytorch-lightning/pull/7652))
 
 
+- Deprecated `DDPPlugin.task_idx` in favor of `DDPPlugin.local_rank` ([#8203](https://github.com/PyTorchLightning/pytorch-lightning/pull/8203))
+
+
 - Deprecated the `Trainer.train_loop` property in favor of `Trainer.fit_loop` ([#8025](https://github.com/PyTorchLightning/pytorch-lightning/pull/8025))
 
 
diff --git a/pytorch_lightning/plugins/training_type/ddp.py b/pytorch_lightning/plugins/training_type/ddp.py
index a24bfc34977cc..cf89a41b93408 100644
--- a/pytorch_lightning/plugins/training_type/ddp.py
+++ b/pytorch_lightning/plugins/training_type/ddp.py
@@ -94,7 +94,7 @@ def __init__(
         self.num_processes = len(self.parallel_devices) if self.parallel_devices is not None else 0
         self._ddp_kwargs = kwargs
         self._has_spawned_children = False
-        self.task_idx = None
+        self._task_idx = None
         self._ddp_comm_state = ddp_comm_state
         self._ddp_comm_hook = ddp_comm_hook
         self._ddp_comm_wrapper = ddp_comm_wrapper
@@ -128,6 +128,18 @@ def sync_batchnorm(self) -> bool:
     def sync_batchnorm(self, sync_batchnorm: bool) -> None:
         self._sync_batchnorm = sync_batchnorm
 
+    @property
+    def task_idx(self) -> Optional[int]:
+        rank_zero_deprecation(
+            f'`{self.__class__.__name__}.task_idx` is deprecated in v1.4 and will be removed in v1.6. Use '
+            f'`{self.__class__.__name__}.local_rank` instead.'
+        )
+        return self._task_idx
+
+    @task_idx.setter
+    def task_idx(self, task_idx: int) -> None:
+        self._task_idx = task_idx
+
     @property
     def distributed_sampler_kwargs(self):
         distributed_sampler_kwargs = dict(num_replicas=(self.num_nodes * self.num_processes), rank=self.global_rank)
diff --git a/tests/deprecated_api/test_remove_1-6.py b/tests/deprecated_api/test_remove_1-6.py
index e92af2f3926af..5fe6bb210dab7 100644
--- a/tests/deprecated_api/test_remove_1-6.py
+++ b/tests/deprecated_api/test_remove_1-6.py
@@ -243,3 +243,9 @@ def test_v1_6_0_rank_zero_warnings_moved():
         rank_zero_warn('test')
     with pytest.deprecated_call(match='in v1.3.7 and will be removed in v1.6'):
         rank_zero_deprecation('test')
+
+
+def test_v1_6_0_ddp_plugin_task_idx():
+    plugin = DDPPlugin()
+    with pytest.deprecated_call(match='Use `DDPPlugin.local_rank` instead'):
+        _ = plugin.task_idx