San Diego / Los Angeles Chargers 2015 On May 2, 2015, Williams was signed as an undrafted free agent by the
San Diego Chargers following the
2015 NFL draft. On September 19, 2015, he was waived. On September 22, 2015, he was signed to the Chargers'
practice squad. On November 21, 2015, he was promoted to the active roster. On January 3, 2016, Williams made his first catch of the season and caught an 80-yard touchdown reception in the regular season finale. He finished the game with two catches for a total of 90 yards and one touchdown in a 20–27 loss to the
Denver Broncos.
2016 In the 2016 season, Williams made two catches for 71 yards in the season opener against
AFC West rival
Kansas City Chiefs. He became the third wide receiver behind
Dontrelle Inman and
Travis Benjamin after starting wide receivers
Keenan Allen and
Stevie Johnson were placed on injured-reserve for the season. The following week, he caught his first touchdown of the season on a 44-yard reception against the
Jacksonville Jaguars in Week 2. On October 9, 2016, he had his first career game with over 100 receiving yards against the
Oakland Raiders. He finished the game with five receptions for 117 yards and a touchdown in the Chargers' 31–34 loss. In Week 7, against the
Atlanta Falcons, he had seven receptions for 140 receiving yards in the 33–30 victory. In Week 10 against the
Miami Dolphins, he had five receptions for 125 receiving yards and one receiving touchdown in the 31–24 loss. Williams finished his second season with 69 catches for 1,059 yards and seven touchdowns.
2017 In 2017, Williams played in all 16 games with 15 starts, recording 43 receptions for 728 yards and four touchdowns.
2018 On March 12, 2018, the Chargers placed a second-round restricted free agent tender on Williams. On April 23, 2018, he signed his tender. In Week 6, he recorded three receptions for 118 receiving yards and two receiving touchdowns in a victory over the
Cleveland Browns. In the 2018 season, he finished with 41 receptions for 653 yards and five touchdowns. In the
Wild Card Round victory over the
Baltimore Ravens, he had two receptions for nine yards. In the
Divisional Round loss to the
New England Patriots, he had five receptions for 94 yards.
Oakland / Las Vegas Raiders 2019 On March 13, 2019, Williams signed a four-year, $44 million contract with the Raiders. Williams made his debut with the Raiders in Week 1 against the Broncos on
Monday Night Football. In the game, Williams caught six passes for 105 yards and a touchdown in the 24–16 win. In Week 2 against the Chiefs, Williams caught five passes for 46 yards and one touchdown as the Raiders lost 28–10. In Week 3 against the
Minnesota Vikings, Williams caught three passes for 29 yards and his third receiving touchdown of the season as the Raiders lost 34–14. In Week 4 against the
Indianapolis Colts, Williams caught three passes for 36 yards and one touchdown in the 31–24 win. This was Williams' fourth consecutive game with a receiving touchdown. Williams was forced to miss the Raiders' next two games due to a foot injury. He made his return in Week 8 against the
Houston Texans. In the game, Williams caught three passes for 91 yards and a touchdown in the 27–24 loss. Overall, Williams finished the 2019 season with 42 receptions for 651 receiving yards and six receiving touchdowns.
2020 season On September 1, 2020, Williams was placed on season-ending
injured reserve after suffering a torn labrum in his shoulder. On February 24, 2021, Williams was released by the Raiders.
Detroit Lions 2021 On March 9, 2021, Williams signed a one-year deal with the
Detroit Lions. He was placed on injured reserve on September 23, 2021, after suffering a concussion in Week 1. He was released on November 5. ==NFL career statistics==