[2] A 3-star recruit, he committed to Brigham Young University (BYU) to play college football over an offer from Boise State.

[6] On August 30, 2012, Williams made his collegiate debut with 15 rushing yards in the win over Washington State.

[25][26] Williams started his final collegiate season in 2016 with 163 rushing yards against Arizona.

[28] On September 30, he rushed for a school-record 286 yards and five touchdowns on 29 carries during a 55–53 win over Toledo.

[30] In his final college game, he was named the MVP of the 2016 Poinsettia Bowl after rushing for 210 yards and a touchdown against Wyoming.

[40] On September 10, 2017, in his NFL debut, Williams had two rushes for nine yards in a 17–9 victory over the Seattle Seahawks.

[56] In the Lions' 2021 regular season opener, he had 110 scrimmage yards in the 41–33 loss to the San Francisco 49ers.

[64] With two rushing touchdowns in the final game of the regular season against the Green Bay Packers in Week 18,[65] Williams set the Lions' single-season touchdown record with 17, surpassing the previous record of 16 set by Barry Sanders in 1991.

[66] He finished the year with career-highs in yards (1,066), touchdowns (17) and carries (262) while playing in all 17 games for the Lions.

[70] Williams failed to record a rushing touchdown during the 2023 season until the Saints' final offensive play against the Atlanta Falcons in Week 18.

[71] While Saints head coach Dennis Allen called for a quarterback kneel to exhaust the final minute of the game, quarterback Jameis Winston instead handed the ball to Williams who scored a one-yard touchdown.

[78] After a game on January 1, 2023, Williams wore a Naruto headband and shirt while giving interviews to reporters, and said that he wanted to go home to play Pokémon Scarlet.

[79] During the Sunday Night Football game against the Packers on January 8, 2023, Williams wore a different Naruto headband and introduced himself as "First Swagg Kazekage, leader of the hidden village of the den", a reference to the anime, drawing immediate reactions on social media.