The southern terminus of the highway is at U.S. Route 43 (US 43) and SR 171 north of Fayette.

The northern terminus of the highway is at an intersection with SR 13 in Haleyville.

SR 129 begins at an intersection with US 43/SR 171 north of Fayette.

Then, SR 129 enters Marion County.

While heading north toward Brilliant, SR 129 has an interchange with Interstate 22 (I-22)/US 78/SR 4 then heads north to Brilliant through wooded areas.