Junior and collegiate career McAvoy played in the 2010
Quebec International Pee-Wee Hockey Tournament with the New York Rangers
minor ice hockey team. In August 2013, McAvoy committed to play college hockey at Boston University. McAvoy played for the
USA Hockey National Team Development Program in the
United States Hockey League for two seasons. During the 2015–16 NCAA men's ice hockey season, BU coach
David Quinn paired McAvoy with star BU defenseman and future fellow NHL player
Matt Grzelcyk, already selected as a third round
2012 NHL entry draft pick by the
Boston Bruins. McAvoy was part of the gold medal-winning team at the
2015 IIHF World U18 Championships. He was also a member of the bronze medal-winning U-20 team at the
2016 World Junior Ice Hockey Championships. Leading up to the
2016 NHL entry draft, McAvoy was highly regarded by scouts and was considered one of the top four defensemen available.
Boston Bruins 2017–18 season On March 29, 2017, McAvoy ended his college hockey career by signing for an amateur try-out with the
Providence Bruins, the Bruins'
AHL affiliate. On April 10, McAvoy signed an entry-level NHL contract. McAvoy's first game was on April 12, 2017, a 2–1 playoff victory over the
Ottawa Senators. Despite having no prior NHL experience, he logged the second most ice time on the team. At a time when four of their top six defenders were injured, McAvoy notched three assists in six games. Following the Bruins' loss to the
Ottawa Senators in the
first round of the playoffs, by mid-June 2017 Bruins legend and Hall of Fame defenseman
Bobby Orr spoke highly of McAvoy's level of talent and work ethic towards succeeding in NHL-level play. McAvoy made his NHL regular season debut on October 5, 2017, the Bruins season opener against the
Nashville Predators. McAvoy got his first regular season points in the game, a goal and an assist in a 4–3 win. On December 18, 2017, McAvoy scored a
Gordie Howe hat trick, which is an unofficial stat where a player gets a goal, an assist, and a fight in one game, against the
Columbus Blue Jackets. The Bruins went on to win the game, 7–2. Shortly after New Years' 2018, McAvoy was operated on for symptoms of what was diagnosed as
supraventricular tachycardia, evidenced by an episode of heart arrhythmia following the Bruins' November 26, 2017 home game against the
Edmonton Oilers. He was expected to take two weeks to fully recover from the ablative procedure used to treat the condition. By January 29, McAvoy had resumed practicing at the
Warrior Ice Arena, only one week (January 22) after completing the atrial ablation procedure. By February 1, McAvoy had resumed full participation with his teammates in Bruins team practice sessions at the Warrior facility. McAvoy returned to NHL play on February 3, 2018, skating some 18:51 of ice time during a 4-1 Bruins home ice win against the
Toronto Maple Leafs. During the first game of a six-game homestand at the TD Garden, on February 27, 2018 McAvoy scored the winning overtime goal against the
Carolina Hurricanes in a 4–3 home ice win, as the youngest Bruins defenseman to ever achieve the feat. On March 31, 2018, prior to a game against the
Florida Panthers, McAvoy was the recipient of the 2017/18 NESN 7th Player Award. Following the Bruins defeat in the second round of the
2018 Stanley Cup playoffs, McAvoy was named to the
senior United States roster to compete at the
2018 IIHF World Championship. At the conclusion of the
2017–18 NHL season McAvoy made the
NHL All-Rookie team while finishing 5th overall in voting for the
Calder Memorial Trophy for rookie of the year.
2018–19 season The following season, after playing in seven games, McAvoy was taken out of the Bruins lineup due to suffering a concussion on October 18 in a game against the
Edmonton Oilers. He was officially placed on the Bruins injured reserve on October 30, and was activated off injured reserve on December 6, after missing 20 games. In his second game back, McAvoy left a game between the Bruins and
Toronto Maple Leafs early after a late hit from Leafs forward
Zach Hyman, but did not suffer any apparent injury. Hyman later received a two-game suspension for the hit. On May 7, 2019, McAvoy was suspended one playoff game for an
illegal check to the head of
Columbus Blue Jackets right winger Josh Anderson during game 6 of the second round. As a result of the suspension, he missed game 1 of the
Eastern Conference final against the
Carolina Hurricanes. McAvoy's sophomore season ended in heartbreak as the Bruins fell to the
St. Louis Blues in Game 7 of the
2019 Stanley Cup Finals. McAvoy recorded eight points in the playoff run.
2019–20 season On September 15, 2019, as a restricted free agent, McAvoy signed a three-year, $14.7 million contract with the Bruins. McAvoy did not take a big step forward in his production in the
2019–20 season, playing alongside NHL legend and Bruins captain
Zdeno Chára. He had only 13 assists by the end of the calendar year, and didn't score his first goal of the season until February 5, 2020, an
overtime winner against the
Chicago Blackhawks. The NHL suspended the season in early March due to the
COVID-19 pandemic, and later announced that the season was cancelled altogether, finishing McAvoy's season with five goals and 27 assists. In the
2020 Stanley Cup playoffs, playing in a bubble due to the pandemic, McAvoy recorded one goal and three assists, as the Bruins fell in five games in the second round to the Lightning. He finished 10th in
Norris Trophy voting, awarded to the league's best defensemen.
2020–21 season In the 2020 offseason, both Chara and
Torey Krug, important parts of the Bruins defense corps, left in the free agency. As a result, McAvoy was seen as a top defenseman on the Bruins roster. He finished fifth in Norris Trophy voting. Offensively, he posted similar totals, with five goals and 25 assists, playing 16 fewer games as the pandemic shortened season started in mid-January rather than late-October. In the playoffs, McAvoy scored an assist per game, with 11 assists in 11 games, adding a goal, which included a three-assist performance in Game 5 of the second round against the
New York Islanders. McAvoy was also the Bruins leader in time-on-ice during their playoff run, which ended in the second round to the Islanders.
2021–22 season Once again set to be a restricted free agent, on October 15, 2021, McAvoy signed an eight-year, $76 million contract extension with the Bruins. At the time, it was the biggest contract in Bruins history. In
2021–22, McAvoy finally took the step forward on offense that the Bruins and their fans were hoping he would. McAvoy scored career highs in both goals and assists, with 10 and 46, respectively. In addition to his offensive numbers, McAvoy continued to be a steady presence on the Bruins blue line, finishing top-5 in Norris voting for the second straight year, and top-10 for the third straight year. It was his best showing, finishing fourth in voting. In seven playoff games, McAvoy kept up his offensive stats with five assists, but the Bruins fell in seven games to the Hurricanes.
2022–23 season On June 3, 2022, the Bruins announced that McAvoy underwent shoulder surgery and would miss six months, sidelining him for the beginning of the
2022–23 season. McAvoy made his season debut on November 10, 2022, and scored a goal in the game. McAvoy and the Bruins set the NHL single-season records with 65 wins and 135 points. The
Florida Panthers upset the Bruins in seven games in the opening round of the
2023 Stanley Cup playoffs. McAvoy had five assists in the series after posting seven goals and 45 assists in the regular season.
2023–24 season On October 30, 2023, McAvoy delivered an illegal check to the head on
Florida Panthers defenseman
Oliver Ekman-Larsson, who was injured on the play. McAvoy received a match penalty, and was suspended for four games.
2024–25 season McAvoy once again entered the season as the Bruins' number one defenseman. Although the Bruins struggled throughout the season, McAvoy remained an anchor on the blue line, and was solid offensively as well. In the Bruins Centennial Game on December 1, 2024, McAvoy scored two goals to help the Bruins beat the
Montreal Canadiens 6-3. From December 14 to December 23, McAvoy had an assist in five straight games. On January 30, 2025, it was announced McAvoy would serve as an
alternate captain for
Team USA at the upcoming
4 Nations Face-Off. It would be the first time that McAvoy had represented the United States in an international hockey competition since the
2018 World Championships. McAvoy entered the tournament with high hopes, but on February 15, 2025, in a
round-robin game against
Team Canada, McAvoy suffered an upper-body injury, and was ruled out of the next game against
Sweden. On February 18, the Bruins announced in a statement that McAvoy had been admitted to
Massachusetts General Hospital to "undergo testing related to an upper-body injury." It was revealed that McAvoy had suffered an infection from the injury, and was week-to-week and subsequently ruled out of the 4 Nations Championship game against Canada. On April 11, 2025, Bruins interim head coach
Joe Sacco confirmed that McAvoy would not return for the season. After the season, it was revealed that McAvoy had suffered a Grade 5 AC joint separation in his shoulder, and was given a pain-killing injection, leading to the infection.
2025–26 season In August 2025 while attending the
Team USA Orientation Camp for the
2026 Olympics, McAvoy spoke about his shoulder injury and indicated that while he had gotten pretty healthy near the end of the 2024-2025 season and he would have played if they made the playoffs, it was for the best to allow his shoulder to heal for longer. McAvoy had a number of face and mouth related injuries during the 2025-2026 season. In mid-November 2025, he broke his jaw and lost four teeth after being hit in the left side of his face by a
slapshot from
Canadiens player
Noah Dobson, then on February 4, 2026 McAvoy was elbowed in the face by
Panthers player
Sandis Vilmanis while wearing a full face shield. On March 5, a puck hit McAvoy on the right side of his mouth chipping a tooth during a game against the
Nashville Predators and on March 10, was hit into the glass by
Kings player
Samuel Helenius with the left side of his mouth taking the brunt of the hit. As of the Olympic winter break during February 2026, McAvoy had played in 45 Bruins games, with four goals and 35 assists, and a career high of 2.15 points per 60 minutes. ==International play==