Williams was selected by the Dallas Cowboys in the eleventh round (283rd overall) of the 1969 NFL/AFL draft as a defensive tackle.
[1] On September 9, he was waived but signed to the team's taxi squad, where he spent all of the 1969 season.
[2] He was given playing time in the 1970 preseason, including a game against the Green Bay Packers where he was scouted.
In the eighth game of the 1970 season against the Baltimore Colts, Bob Brown was switched from left defensive end to tackle, in order for Williams to move into the starting lineup.
Nicknamed "Big Cat", his best season in the NFL came in 1972, when according to the Packers media he led the team with 10.5 sacks.
In 1977, he was displaced by rookie Mike Butler and played mostly as a reserve defensive tackle.