Thomas was selected by the Bills in the second round of the 1988 NFL draft, where he spent all but one season of his professional career.

Thomas' efforts helped his team make a record four consecutive Super Bowl appearances from 1991 to 1994, although the Bills lost each game.

He formerly resided in the Willow Park II subdivision, located southeast of the Fort Bend Tollway and Beltway 8.

Thomas attended college at Oklahoma State University where he was an upperclassman teammate of running back Barry Sanders.

Thomas led the Big Eight in rushing and scoring in 1985 and 1987 and was voted the conference's Offensive Player of the Year both seasons.

From 1984 to 1987, Thomas carried the ball a remarkable 897 times for the Cowboys, the most rushing attempts in a career in Oklahoma State history.

[4] In the 1987 Sun Bowl, Thomas ran for 157 yards and four touchdowns in the 35–33 comeback victory over West Virginia, keeping sophomore Barry Sanders on the sidelines for the majority of the game.

Thomas left OSU as the school's all-time leading rusher and his number 34 (chosen in honor of Earl Campbell and Walter Payton)[5] is one of only three jerseys retired at Oklahoma State.

[9] Thomas is well known as part of the offense that included Jim Kelly and Andre Reed, which led the Bills to four straight Super Bowl appearances.

Thomas is the only player in NFL history to lead the league in total yards from scrimmage for four consecutive seasons.

Walter Payton, Marshall Faulk, Marcus Allen, Ricky Watters, Tiki Barber, Warrick Dunn and LaDainian Tomlinson are the other six.

Thomas is also one of five running backs to have rushed for over 1,000 yards in eight consecutive seasons along with Curtis Martin, Barry Sanders, Emmitt Smith and Tomlinson.

He would have likely won the Super Bowl MVP award, but the Bills lost the game 20-19 when kicker Scott Norwood missed a 47-yard field goal attempt with eight seconds remaining.

He was a reliable target as a receiver out of the backfield, catching seven passes for 52 yards but he lost two fumbles that led to ten Dallas points.

[16] Thomas signed with the Miami Dolphins during the 2000 off-season, after the Bills had released him to clear space under the salary cap.

Thomas, Steve Tasker, Andre Reed, Bruce Smith, Don Beebe, and Jim Kelly were the subject of the 30 for 30 film, Four Falls of Buffalo.