Before the 2006 season, Beason joined the Miami track-and-field team. He competed on the indoor squad during the spring, finishing 18th at the ACC Indoor Track and Field Championships with a season best mark of 6.50 meters in the long jump.
Beason was drafted 25th overall in the 2007 NFL Draft by the Carolina Panthers. Beason had a great rookie season, finishing second behind Patrick Willis in tackles for a rookie with 140. He finished second in the NFL Defensive Rookie of the Year voting behind Willis, receiving two votes. During Beason's second year he was selected to his first Pro Bowl and was an APAll-Pro selection after recording 138 tackles and three interceptions. In the 2009 season Beason recorded three sacks, three interceptions, a forced fumble, and 141 tackles, including 111 solo tackles. As a result, Beason was a second team pick on the 2009 All-Pro Team, and also received a spot in the Pro Bowl when Patrick Willis backed out due to injury. Due to an injury to outside linebacker Thomas Davis, who was placed on the Physically Unable to Perform list, Beason volunteered to move to the outside linebacker position while Davis recovered. However, Davis was not taken off the list by the Panthers, and Beason had to assume the role further until Dan Connor, who had taken over the inside linebacker position, had a season-ending injury, thus moving Beason back inside. Due to him switching positions, he finished the season with the worst statistical performance of his career, recording only 121 tackles (9 less than fellow Panther James Anderson and the first time in his career he did not place first in team tackles). However, Beason was rewarded for his temporary switch to the position, and was designated a Pro Bowl alternate at the outside linebacker position, and later was awarded a spot when Lance Briggs backed out due to an injury.
On July 28, 2011, Beason and the Panthers agreed to terms on a deal that would make him the highest-paid middle linebacker in NFL history. The deal was worth $50 million over 5 years, with $25 million guaranteed. On September 14, Beason was placed on the injured reserve list with an injured left Achilles tendon.However in the 2012 NFL season, Beason lost his middle linebacker starting position to Boston College draft pick Luke Kuechly, who would win the Defensive Rookie of the year for the 2012 season. After starting the first two games of the season, Beason lost his starting job to Chase Blackburn. On October 4, 2013, he was traded to the New York Giants. The trade involved the Carolina Panthers trading Beason for a 7th round pick to the Giants.
Beason's play significantly improved as a member of the Giants; in his 12 games with the Giants in the 2013 season they went 7-4 (after an 0-4 start), and Beason had 93 tackles. On March 12, 2014, Beason and the New York Giants came to an agreement on a new contract, signing a three year $16.8 million deal. Beason tore a ligament and fractured the sesamoid bone in his toe in a June practice and missed all of training camp and all five of the Giants' preseason games. He played in the first two games of the season but reinjured the toe and missed the next three before returning to play on a limited basis against the Eagles in Week 6 and Cowboys in Week 7. After his visit with doctors, Beason said in a radio interview that he might have to have the season-ending toe surgery to finally take care of the problem, and that turned out to be the case. On November 7, 2015, Beason was placed on the Giants' injured reserve for ankle and knee injuries, after appearing in only 5 of the Giants eight games.