I-49 begins its journey in Lafayette concurrent with U.S. Route 167 from I-10 to Opelousas at Exit 23. At Lafayette, motorists continuing southbound see the interstate highway change to U.S. 167 (Evangeline Thruway), a major thoroughfare taking travelers towards the heart of Lafayette. North of Lafayette, motorists on I-49 will parallel the ancient Mississippi river bed north of Carencro, and through Grand Coteau, just south of Opelousas.
After leaving Opelousas, I-49 traverses the relative flat, fertile farmlands until reaching Alexandria. From there, the highway roughly follows the Red River and Louisiana 1, bypassing the historic city of Natchitoches to the west on its way to Shreveport. At Shreveport, the highway parallels a railroad line just to the east until its terminus at I-20 southwest of downtown.