The narrow-headed garter snake, Thamnophis rufipunctatus, is a species of nonvenomous garter snake that is endemic to the southwestern United States. Its common names also include narrowhead garter snake and narrowhead watersnake.

Chiasson and Lowe (1989) suggested the species be included in the genus Nerodia (watersnakes) due to its highly aquatic nature, however, this classification was later rejected based on genetic data.

The Madrean narrow-headed garter snake and Southern Durango spotted garter snake were at times considered subspecies of the narrow-headed garter snake, but are now given full species status based on genetic analysis.

The scientific name Thamnophis rufipunctatus is a combination of Ancient Greek and New Latin that means "bush snake punctuated with red". The generic name Thamnophis is derived from the Greek "thamnos" (bush) and "ophis" (snake) and the specific name rufipunctatus is derived from the New Latin "rufi-" (red) and "punctatus" (punctuated), referring to the snake's reddish-brown spots.

It is found in Arizona and New Mexico at or near the Mogollon Rim, mainly in canyon-bound headwaters of the Gila and San Francisco rivers and their tributaries.

It is not thought to occur in Mexico. Populations in Mexico that were previously considered subspecies of Thamnophis rufipunctatus are now reclassified as separate species.

The snake is blue-grey to olive-grey, or greenish to brown, and it has brown, orange, or black spots on the back. The total length of adults is 81–112 cm (32–44 in) (about 81–112 cm). Its most notable feature is its long, narrow snout, resulting in a rather triangular-shaped head.

It has eight or 9 upper labial scales, one of which enters the eye, two or three preocular scales, two to four postoculars, and one anterior temporal scale. The keeled dorsal scales are arranged in 21 rows at midbody. Ventrals number 152–177; the anal plate is entire; the subcaudals number 65–87, and are divided.