The New England Patriots drafted Cannon in the fifth round, with the 138th pick, acquired in a trade from the Houston Texans. Cannon's late selection in the draft is widely attributed to his being diagnosed with non-Hodgkin lymphoma pre-draft. Weighing in at 358 pounds at the NFL Combine, Cannon is the heaviest player ever drafted by the Patriots, and the second-heaviest player in team history after nose tackleTed Washington, who played with the team in the 2003 season. Although he played offensive tackle throughout his TCU career, the Patriots listed Cannon as an offensive guard when announcing the pick. Cannon began the 2011 season on the Non-Football Injury list as he recuperated from his chemotherapy treatment, which took place during the NFL lockout. Cannon was activated to the 53-man roster after the Patriots' Week 10 game against the New York Jets, and saw his first snaps in the NFL at right tackle on the Patriots' final drive against the Kansas City Chiefs in Week 11. Cannon was selected as the Patriots' 2011 recipient for the Ed Block Courage Award. Cannon played in all 18 of the Patriots' regular and postseason games during the 2012 NFL season, including one start in place of right tackle Sebastian Vollmer. After Vollmer went on injured reserve in late October of the 2013 season, Cannon started the rest of the season for New England at right tackle. Cannon began the 2014 season as the Patriots' starting left guard but struggled in the first three games and was moved back to his previous role as a swing tackle after rookie Bryan Stork took over as the starting center. On Dec 11, Cannon signed a two-year extension worth up to $9 million, including a $3.2 million signing bonus. On February 1, 2015, Cannon was a member of the New England Patriots when they won Super Bowl XLIX. In the 2015 season, Cannon appeared in the fewest regular-season games—12—since his rookie season because of a toe injury. Nonetheless, he also started the most games of his career at eight. Cannon entered the 2016 Patriots training camp in what he called "the best shape of his life." After struggling the previous season while dealing with the toe injury, his play improved significantly during the 2016 season. After starting right tackle Sebastian Vollmer had shoulder surgery during the offseason was ruled out for the season, Cannon became the starting right tackle. With his significant improvement and performance through the first 11 games of the season, Cannon signed a five-year, $32.5 million contract extension with the Patriots through 2021. For his performance in the 2016 season, Cannon was named second-team All-Pro by Pro Football Focus and The Associated Press. On February 5, 2017, Cannon was part of the Patriots team that won Super Bowl LI. In the game, the Patriots defeated the Atlanta Falcons by a score of 34–28 in overtime. The game featured the first overtime game in Super Bowl history and the largest comeback in the Super Bowl. Cannon started the 2017 season as the Patriots' starting right tackle. He started seven games before suffering an ankle injury in Week 8. He missed the next five games before being placed on injured reserve on December 13, 2017. The Patriots were able to reach Super Bowl LII without Cannon, but failed to repeat as Super Bowl Champions after losing 41-33 to the Philadelphia Eagles. Cannon entered 2018 as the Patriots starting right tackle. He missed Week 2 with a calf injury and Weeks 9 and 10 with a head injury. Overall he started 13 games in 2018. With Cannon, the Patriots were able to reach Super Bowl LIII where they defeated the Los Angeles Rams 13-3. On September 9, 2019, in the Patriots Week 1 matchup against the Pittsburgh Steelers, Cannon sustained a shoulder injury in the fourth quarter, which may cause him to miss a couple of months. On July 28, 2020, Cannon announced his decision to opt out of the 2020 season, due to concerns over the ongoing COVID-19 pandemic.
Personal life
Cannon was born in Odessa, Texas. He graduated from TCU with a communications degree and on top of football was also all conference in the shot put. Cannon was diagnosed with cancer in 2011 after a biopsy was conducted at the request of two different NFL teams. Despite the mass's having been ruled as benign in 2006, it was found to be cancerous. Cannon underwent treatment and has now been in remission for seven years. Marcus Cannon and his wife Alyssa were married in 2012. The couple has three children.