On April 30, 2012, Bellamy signed with the Kansas City Chiefs as an undrafted free agent. On August 31, 2012, he was released from the roster. On September 1, 2012, he was signed to the practice squad. On December 8, 2012, he was promoted to the active roster. He was released by the team on August 31, 2013.
On November 21, 2013, two days after his release from the Chargers, Bellamy was signed by the Washington Redskins to their practice squad. On November 26, 2013, Bellamy was promoted to the 53-man roster. He was released by the team on April 5, 2014.
Bellamy was acquired off waivers by the Chicago Bears on April 8, 2014. The Bears signed him to the team's practice squad on September 1, 2014, after waiving him earlier for final roster cuts. He was activated on September 13, 2014.
2015
On September 20, 2015, Bellamy caught his first career touchdown against the Arizona Cardinals. On October 11, 2015, Bellamy caught a career-high 6 receptions against the Kansas City Chiefs. On November 22, 2015, Bellamy caught 4 passes for a then career-high 57 yards against the Denver Broncos. On December 6, 2015, Bellamy had his first start, against the San Francisco 49ers, catching a pass for 16 yards.
2016
On April 18, 2016, Bellamy signed his exclusive rights tender offer. He re-signed with Chicago on a one-year deal worth $760,000. On November 27, 2016, Bellamy caught four passes for 41 yards against the Tennessee Titans, but struggled with drops as the Bears lost 27–21. On December 4, 2016, Bellamy caught four passes for a career-high 93 yards against the San Francisco 49ers.
2017
On March 6, 2017, Bellamy re-signed with the Bears. He caught a 46-yard touchdown against the Green Bay Packers on November 12, his second-longest touchdown of his career. On December 16, Bellamy caught five passes for a season-high 70 yards against the Detroit Lions. He played 15 games with seven starts, finishing with a career-high 24 receptions for 376 yards, good for second on the team behind Kendall Wright.
2018
He re-signed with the Chicago Bears for the 2018 season on a one-year contract worth $1,906,000. On September 30, 2018, Bellamy caught his first touchdown of the season in the 48–10 victory over the Tampa Bay Buccaneers. On December 15, Bellamy was fined $10,026 for a chop-block on Los Angeles Rams lineman Aaron Donald. In week 16 against the San Francisco 49ers, Bellamy was ejected after fighting cornerback Richard Sherman. They started fighting after 49ers safety Marcell Harris made a late hit on quarterback Mitchell Trubisky and wide receiver Anthony Miller joined the effort. In addition, Sherman and Miller were also ejected from the game. Before Bellamy was ejected, he had just one reception for 6 receiving yards. The Bears would go on to win 14-9. Bellamy ended the year with 14 receptions for 117 yards and a touchdown. In the Bears' playoff defeat to the Philadelphia Eagles, he recorded a 34-yard catch that set up the Bears' lone offensive touchdown of the game.
On March 15, 2019, Bellamy signed a two-year, $5 million contract with the New York Jets. He was placed on injured reserve on November 5. Bellamy was placed on the reserve/physically unable to perform list on May 5, 2020, ending his 2020 season.
