The 25-mile (40 km) road, located entirely within Lea County, begins at US 380 near Tatum and ends at the Texas state line where the road meets the numerically continuous Texas State Highway 125 southwest of Bledsoe, TX.

The road proceeds to the north and then the northeast before NM 508 branches off to the west toward Crossroads.

[3] NM 125 passes through mostly agricultural lands and oil and gas fields across the largely flat and featureless terrain of the Llano Estacado.

[4][5] NM 125 was created sometime after 1941[6] probably in the early 1950s as Texas began the uncommon process of unofficially signing SH 125's predecessor route, Farm to Market Road 769, as a numerically continuous state highway in 1955.

Geographic data related to New Mexico State Road 125 at OpenStreetMap