He played college football for the Clemson Tigers and was selected by the Los Angeles Chargers seventh overall in the 2017 NFL draft.

Williams attended Lake Marion High School & Technology Center in Santee, South Carolina, where he played on the football team.

[1][10] On January 10, 2017, hours after Clemson defeated Alabama 35–31 for the national championship, Williams announced that he would forgo his senior year and enter the 2017 NFL draft.

[12] Coming out of Clemson, Williams was considered a top prospect and projected as a first round pick by the majority of draft experts and analysts.

[13][14][15] The Los Angeles Chargers selected Williams in the first round with the seventh overall pick in the 2017 NFL draft.

[23] On July 30, 2017, it was announced by head coach Anthony Lynn that Williams was expected to miss the entire training camp due to his back injury.

He made his first career reception on a 15-yard pass by quarterback Philip Rivers in the fourth quarter of their 17–16 victory at the Oakland Raiders, before being tackled by safety Karl Joseph.

[33] In Week 9 against the Green Bay Packers, Williams caught three passes for a season-high 111 yards in the 26–11 win.

[39] In Week 5 against the New Orleans Saints on Monday Night Football, Williams recorded five catches for 109 yards and two touchdowns during the 30–27 overtime loss.

[40] In Week 16 against the Broncos, Williams recorded his first career interception off a pass thrown by Drew Lock on a Hail-Mary attempt with no time left in the game to secure a 19–16 win for the Chargers.

[46] Williams had a breakout season in 2021, setting career highs in receptions (76), targets (129), and yards (1,146) while scoring nine touchdowns.

[55] In Week 3, against the Minnesota Vikings, Williams suffered an ACL tear in the third quarter, and was ruled out for the season.

[60][61] In Week 6, Williams was criticized by quarterback Aaron Rodgers for running the wrong route on a pass intended for him, which resulted in a game-clinching interception in a loss to the Buffalo Bills.

[63] On November 5, 2024, the Jets traded Williams to the Pittsburgh Steelers in exchange for a fifth-round pick in the 2025 NFL draft.