In his first season for South Florida, Williams spent time at both linebacker and on special teams, appearing in all 13 games. He recorded 28 tackles and one tackle for a loss. He made one start for the Bulls, against the Connecticut Huskies, tallying five tackles and a tackle for a loss. During the 2010 International Bowl against Northern Illinois, Williams made four tackles, helping South Florida win 27–3 in the final edition of the game. The following year, his senior season, Williams was named a team captain for the Bulls as well as a starter at outside linebacker, starting every game for the team. He led the team with 71 tackles and also recorded 11 tackles for a loss, one interception, and 2.5 sacks. Against Rutgers, he recorded a career-high 11 tackles and also recorded seven tackles against both Miami and Connecticut. Williams finished his career at South Florida with three tackles in the 2010 Meineke Car Care Bowl, which South Florida won 31–26 over the Clemson Tigers. He was named second–team All–Big East after the season. Williams finished his career at South Florida with 231 tackles, eight sacks, 35 tackles for a loss, three forced fumbles, two fumble recoveries, and three interceptions.
Williams appeared in the ESPN documentary "The Dotted Line", filmed in the months leading up to the 2011 NFL draft. The program depicted the relationship between Williams and his first agent, Eugene Lee of ETL Associates, as well as Williams's decision to dump ETL after the draft. Williams was selected in the sixth round with the 202nd overall pick by the New York Giants in the 2011 NFL Draft, once again re-uniting him with Jason Pierre-Paul, his teammate at Fort Scott Community College and the University of South Florida. According to Ohm Youngmisuk of ESPN, "Williams caught the Giants' attention with his athleticism, speed and untapped potential." On July 29, Williams signed his rookie contract with the Giants. During training camp, Williams has mainly seen time with third–team defense. In his rookie season, Williams had 78 tackles. He played in all 16 games and made 2 starts. During the NFC Championship game on January 22, 2012 between the Giants and the San Francisco 49ers, Williams stripped 49ers punt returner Kyle Williams during a punt return and the Giants recovered it in field goal range, which led to the game-winning field goal by Lawrence Tynes and put the Giants in Super Bowl XLVI, their second Super Bowl in four years.