diff --git a/pandas/_libs/tslibs/timedeltas.pyx b/pandas/_libs/tslibs/timedeltas.pyx
index 6707d63dab517..d36953052c472 100644
--- a/pandas/_libs/tslibs/timedeltas.pyx
+++ b/pandas/_libs/tslibs/timedeltas.pyx
@@ -300,6 +300,12 @@ cdef int64_t _numeric_to_td64ns(
     if is_integer_object(item) and item == NPY_NAT:
         return NPY_NAT
 
+    # Early overflow guard for scalar numeric input
+    if unit=="ns" and is_integer_object(item):
+        if item>9223372036854775807 or item <-9223372036854775808:
+            raise OutOfBoundsTimedelta(
+                f"Cannot cast {item} from {unit} to 'ns' without overflow."
+            )
     try:
         ival = cast_from_unit(item, unit, out_reso)
     except OutOfBoundsDatetime as err:
diff --git a/pandas/tests/scalar/timedelta/test_constructors.py b/pandas/tests/scalar/timedelta/test_constructors.py
index 38c0de58d5291..c48d74cd515a3 100644
--- a/pandas/tests/scalar/timedelta/test_constructors.py
+++ b/pandas/tests/scalar/timedelta/test_constructors.py
@@ -3,7 +3,7 @@
 
 import numpy as np
 import pytest
-
+import pandas as pd
 from pandas._libs.tslibs import OutOfBoundsTimedelta
 from pandas._libs.tslibs.dtypes import NpyDatetimeUnit
 from pandas.errors import Pandas4Warning
@@ -778,3 +778,7 @@ def test_parsed_unit():
     # 7 digits after the decimal
     td = Timedelta("1 Day 2:03:04.0123450")
     assert td.unit == "ns"
+def test_to_timedelta_overflow_raises():
+    msg = "Cannot cast .* from ns to 'ns' without overflow"
+    with pytest.raises(OutOfBoundsTimedelta, match=msg):
+        pd.to_timedelta(10**20, unit="ns")