diff --git a/tests/reasoning/test_nemotron_v3_reasoning_parser.py b/tests/reasoning/test_nemotron_v3_reasoning_parser.py
new file mode 100644
index 000000000..3fe383a08
--- /dev/null
+++ b/tests/reasoning/test_nemotron_v3_reasoning_parser.py
@@ -0,0 +1,150 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+from typing import TypedDict
+
+import pytest
+import regex as re
+
+from tests.reasoning.utils import run_reasoning_extraction
+from vllm.entrypoints.openai.chat_completion.protocol import ChatCompletionRequest
+from vllm.reasoning import ReasoningParser, ReasoningParserManager
+
+parser_name = "nemotron_v3"
+
+
+class ReasoningCase(TypedDict):
+    output: str
+    reasoning: str | None
+    content: str | None
+
+
+class FakeNemotronTokenizer:
+    def __init__(self):
+        self._vocab = {
+            "<think>": 1,
+            "</think>": 2,
+        }
+        self._pattern = re.compile(r"(<think>|</think>)")
+
+    def get_vocab(self) -> dict[str, int]:
+        return self._vocab
+
+    def tokenize(self, text: str) -> list[str]:
+        tokens: list[str] = []
+        for part in self._pattern.split(text):
+            if part:
+                tokens.append(part)
+        return tokens
+
+    def convert_tokens_to_string(self, tokens: list[str]) -> str:
+        return "".join(tokens)
+
+
+@pytest.fixture
+def tokenizer():
+    return FakeNemotronTokenizer()
+
+
+@pytest.mark.parametrize(
+    "streaming,param_dict",
+    [
+        pytest.param(
+            False,
+            {
+                "output": "This is a reasoning section</think>This is the rest",
+                "reasoning": "This is a reasoning section",
+                "content": "This is the rest",
+            },
+            id="without_start_token",
+        ),
+        pytest.param(
+            True,
+            {
+                "output": "This is a reasoning section</think>This is the rest",
+                "reasoning": "This is a reasoning section",
+                "content": "This is the rest",
+            },
+            id="without_start_token_streaming",
+        ),
+        pytest.param(
+            False,
+            {
+                "output": "<think>This is a reasoning section</think>This is the rest",
+                "reasoning": "This is a reasoning section",
+                "content": "This is the rest",
+            },
+            id="with_start_token",
+        ),
+        pytest.param(
+            True,
+            {
+                "output": "<think>This is a reasoning section</think>This is the rest",
+                "reasoning": "This is a reasoning section",
+                "content": "This is the rest",
+            },
+            id="with_start_token_streaming",
+        ),
+    ],
+)
+def test_nemotron_v3_reasoning(
+    tokenizer: FakeNemotronTokenizer,
+    streaming: bool,
+    param_dict: ReasoningCase,
+):
+    output = tokenizer.tokenize(param_dict["output"])
+    model_output = [tokenizer.convert_tokens_to_string([token]) for token in output]
+    parser: ReasoningParser = ReasoningParserManager.get_reasoning_parser(parser_name)(
+        tokenizer
+    )
+
+    reasoning, content = run_reasoning_extraction(
+        parser, model_output, streaming=streaming
+    )
+
+    assert reasoning == param_dict["reasoning"]
+    assert content == param_dict["content"]
+
+
+def test_nemotron_v3_without_thinking_returns_content(
+    tokenizer: FakeNemotronTokenizer,
+):
+    parser_cls = ReasoningParserManager.get_reasoning_parser(parser_name)
+    parser = parser_cls(tokenizer)
+    request = ChatCompletionRequest(
+        model="test-model",
+        messages=[],
+        chat_template_kwargs={"enable_thinking": False},
+    )
+
+    reasoning, content = run_reasoning_extraction(
+        parser,
+        ["This is plain content"],
+        request=request,
+        streaming=False,
+    )
+
+    assert reasoning is None
+    assert content == "This is plain content"
+
+
+def test_nemotron_v3_with_thinking_keeps_truncated_reasoning(
+    tokenizer: FakeNemotronTokenizer,
+):
+    parser_cls = ReasoningParserManager.get_reasoning_parser(parser_name)
+    parser = parser_cls(tokenizer)
+    request = ChatCompletionRequest(
+        model="test-model",
+        messages=[],
+        chat_template_kwargs={"enable_thinking": True},
+    )
+
+    reasoning, content = run_reasoning_extraction(
+        parser,
+        ["This is truncated reasoning"],
+        request=request,
+        streaming=False,
+    )
+
+    assert reasoning == "This is truncated reasoning"
+    assert content is None
diff --git a/vllm/reasoning/__init__.py b/vllm/reasoning/__init__.py
index df75e8584..8c78db6f1 100644
--- a/vllm/reasoning/__init__.py
+++ b/vllm/reasoning/__init__.py
@@ -68,6 +68,10 @@ _REASONING_PARSERS_TO_REGISTER = {
         "mistral_reasoning_parser",
         "MistralReasoningParser",
     ),
+    "nemotron_v3": (
+        "nemotron_v3_reasoning_parser",
+        "NemotronV3ReasoningParser",
+    ),
     "olmo3": (
         "olmo3_reasoning_parser",
         "Olmo3ReasoningParser",
diff --git a/vllm/reasoning/nemotron_v3_reasoning_parser.py b/vllm/reasoning/nemotron_v3_reasoning_parser.py
new file mode 100644
index 000000000..a929793bf
--- /dev/null
+++ b/vllm/reasoning/nemotron_v3_reasoning_parser.py
@@ -0,0 +1,32 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+from vllm.entrypoints.openai.chat_completion.protocol import (
+    ChatCompletionRequest,
+)
+from vllm.entrypoints.openai.responses.protocol import (
+    ResponsesRequest,
+)
+from vllm.reasoning.deepseek_r1_reasoning_parser import DeepSeekR1ReasoningParser
+
+
+class NemotronV3ReasoningParser(DeepSeekR1ReasoningParser):
+    """
+    Reasoning parser for Nemotron V3 models.
+    """
+
+    def extract_reasoning(
+        self, model_output: str, request: ChatCompletionRequest | ResponsesRequest
+    ) -> tuple[str | None, str | None]:
+        reasoning_content, final_content = super().extract_reasoning(
+            model_output, request
+        )
+        chat_template_kwargs = getattr(request, "chat_template_kwargs", None)
+
+        if (
+            chat_template_kwargs
+            and chat_template_kwargs.get("enable_thinking") is False
+            and final_content is None
+        ):
+            reasoning_content, final_content = final_content, reasoning_content
+
+        return reasoning_content, final_content