Amateur Upon entering high school age, Dumoulin played hockey for the
Biddeford High School (BHS) Tigers where he helped them win back-to-back state championships. During that time frame, he accumulated 107 points through 48 games. As a result of his successful play, he left BHS as a junior to play for the
New Hampshire Junior Monarchs, a Tier III Junior A team. Part of the reason Dumoulin left BHS was that he felt playing junior hockey instead of high school hockey would lead to a better path to Division I collegiate hockey. Although he left, his brother John remained at BHS before retiring upon graduating. As a senior during the 2008–09 season, Dumoulin helped the team capture the regular-season championship and was named the EJHL’s Defensive Player of the Year. Due to his success on the ice, Dumoulin was courted by his home state university
University of Maine,
Providence College,
Northeastern University,
Harvard University,
University of New Hampshire, and
Boston College (BC).
Collegiate Prior to starting his freshman season at BC, Dumoulin was drafted in the second round, 51st overall, by the
Carolina Hurricanes in the
2009 NHL entry draft. Following the draft, Dumoulin enrolled at BC's
Carroll School of Management while playing for the
Boston College Eagles men's ice hockey team which competed in the
NCAA's
Division I in the
Hockey East conference. He had originally been on school visits to Providence College, Northeastern University, Harvard University, University of New Hampshire, Boston College, and the University of Maine before being offered a scholarship to BC. In his freshman year, Dumoulin recorded 12 points and led the team with a plus-40 rating. He also helped the Eagles qualify for the
2010 NCAA Frozen Four and was selected for the
All-Tournament Team following their win. Dumoulin returned to the Eagles for the 2010–11 season for his sophomore year. He began the season strong, recording 10 points through 16 games, before being selected for Team USA at the
2011 World Junior Ice Hockey Championships. He returned from the tournament with a bronze medal and continued to produce offensively. He finished the season with three goals and 30
assists for 33
points through 37 games. He finished the season earning
American Hockey Coaches Association (AHCA)
All-Hockey East Teams First Team honors and earned both
Hockey East Best Defensive Defenseman honor and the Bob Monahan Award as the top defenseman in New England. During the 2011 offseason, Dumoulin attended the Hurricanes Conditioning Camp. Upon returning to the Eagles for the
2011–12 season, Dumoulin tallied seven goals and 28 points through 44 games During the Final against Ferris State, Dumoulin tallied a goal in the first period to help lead the team to a 4–1 win. Prior to the tournament, Dumoulin was named a finalist for the 2012
Hobey Baker Award as he led all Hockey East defensemen in scoring. Following the Eagles' NCAA win, Dumoulin was again selected for the All-Tournament Team alongside teammates
Johnny Gaudreau and
Parker Milner. On April 10, 2012, the Hurricanes signed Dumoulin to an
entry-level contract.
Professional Pittsburgh Penguins in 2013 Upon concluding his collegiate career, Dumoulin attended the Penguins' annual Development Camp. After attending the camp, Dumoulin was re-assigned to their
American Hockey League (AHL) affiliate, the
Wilkes-Barre/Scranton Penguins, to begin the
2012–13 season. In his first season with the WBS Penguins, Dumoulin tallied six goals and 18 assists for 24 points through 79 games. He subsequently made his NHL debut in a December 14, game against the
Detroit Red Wings. As a result of numerous penalties taken during the game, Dumoulin played 18:10 minutes of ice time. He scored his first NHL point, an assist on
Chris Conner's goal, in a game two days later against netminder
Jonathan Bernier of the
Toronto Maple Leafs. He was re-assigned to the AHL after recording one assist in six games. Dumoulin rejoined the WBS Penguins for their
2014 Calder Cup playoffs run and recorded 12 points through 17 games. As a result of numerous injuries to the Penguins lineup, Dumoulin and
Bryan Rust joined the teams' lineup in December. In his tenth NHL game, Dumoulin scored his first career NHL goal against
Evgeni Nabokov of the
Tampa Bay Lightning, on December 15, 2014. After Rust also scored his first NHL goal that night, the two became the first Penguins pair to reach this milestone at the same time since 2006. Upon rejoining the AHL, Dumoulin led all team defensemen in assists and points with 29 and 33. Due to his play, he earned another recall to the NHL level in April 2015. He competed with the Penguins during their first-round matchup against the
New York Rangers, skating an average of 14:06 minutes a night through five postseason games. On July 9, 2015, Dumoulin signed a two-year one-way contract to remain with the Penguins organization. During the 2015 offseason, Dumoulin remained in Boston with two of his former Eagles teammates to continue off-ice workouts under
strength and conditioning coach Russ DeRosa. He also began skating with High End Hockey at the Breakaway Center. Once the
2015–16 season began, Dumoulin played alongside
Ben Lovejoy and became the teams' most consistent defender. Dumoulin was eventually paired with
Trevor Daley and continued as one of Pittsburgh's most consistent defensemen with 16 assists and a plus-11 rating by March. Once the postseason began, Dumoulin scored his first NHL playoff goal in game five of the Eastern Conference Final against the Tampa Bay Lightning. His goal, which came with 0.7 seconds left in the first period, helped lead the Penguins to an overtime loss. Despite this loss, he helped the Penguins push for game seven and played alongside veteran
Kris Letang. Dumoulin's second post-season goal came during game six of the
2016 Stanley Cup Final against the
San Jose Sharks to help the team win the
Stanley Cup. With a 3–1 win over the San Jose Sharks,
Biddeford-born Dumoulin became the first Maine-born NHL player to hoist the
Stanley Cup. Following the Stanley Cup win, Dumoulin returned to Boston and signed up for a summer course in order to finish his bachelor’s degree in marketing. Upon completing the class, he was one course away from graduating. Dumoulin returned to the Penguins lineup for the
2016–17 season with an expectation of assuming a bigger role. Dumoulin began the season tallying seven assists through 35 games before sustaining a broken jaw during a game against the
New Jersey Devils in late December. As such, he was expected to miss four to six weeks in order to recover. He was activated off injured reserve on January 24, 2017, after missing 10 games and became the Penguins top defenceman following an injury to Kris Letang. He finished the regular season with one goal and 14 assists for 15 points through 70 games. As the Penguins once again qualified for the
Stanley Cup playoffs, Dumoulin helped the team win their second Stanley Cup on June 11, 2017. It was later revealed that Dumoulin had been playing through a hand injury that occurred after taking a slapshot off the hand in game five of the Eastern Conference quarterfinals. On July 24, 2017, the Penguins re-signed Dumoulin to a six-year, $24.6 million contract worth $4.1 million annually. The deal began during the
2017–18 season and runs through the
2022–23 season. In the first year of his new contract, Dumoulin set career highs in goals, with five, and points, with 18, through 80 games. He had missed only two games during the season following a concussion. Following his return, Dumoulin also completed his bachelor's degree in marketing from BC. As the Penguins once again qualified for the Stanley Cup playoffs, they met with the
Philadelphia Flyers in Round 1. Throughout the series, Dumolin continued to produce and recorded multiple points in the first two games. The Penguins eventually beat the Flyers in Game six to tie their franchise record with nine playoff series wins. Dumoulin returned to the lineup for Round 2 against the
Washington Capitals but went through the NHL's concussion protocol following a hit in game two. The Penguins would end up falling to the Capitals in six games. Dumoulin re-joined the Penguins for the
2018–19 pre-season but suffered an upper body injury during a game against the
Columbus Blue Jackets. He missed a week before returning in a full-contact jersey at Penguins practice on October 3. He remained a consistent member of the Penguins lineup before being diagnosed with a concussion following their
2019 NHL Stadium Series matchup against the Flyers. He returned to the lineup after missing three games. As Letang,
Olli Määttä, and
Chad Ruhwedel remained out due to injuries, Dumoulin's time on ice increased and he logged over 20 minutes of ice time during a game against the
Buffalo Sabres. Although he would miss the last three games of the regular season with a lower-body injury, Dumoulin recorded a career high 23 points through 76 games. He returned to the Penguins lineup shortly thereafter and tallied one goal and six assists in 23 games before undergoing ankle surgery. Dumoulin subsequently missed 33 games before returning to Penguins practice on February 25, 2020. After spending the majority of the previous season battling injuries, Dumoulin returned to the Penguins lineup to begin the
2020–21 season. Although he missed 15 games with a lower-body injury, Dumoulin improved the Penguins blueline who went 29-9-3 with him in the lineup. Dumoulin tallied four goals and 14 points in 41 games to rank fifth amongst goals scored by defencemen and fifth-most points. He finished the shortened 2020–21 season logging an average of 22 minutes, 21 seconds per game, including a team-best 2:45 on the penalty kill. Head coach Mike Sullivan praised Dumoulin's defensive abilities calling him "not just an ‘off-the-glass-and-out’ guy." Prior to the start of the
2021–22 season, Dumoulin trained with
John Marino in Boston. Together, they would skate before working out at the home gym in Dumoulin's garage in Charlestown. Once the season began, Dumoulin played eight games before being placed on the NHL's COVID-19 protocol list.
Seattle Kraken On July 1, 2023, Dumoulin left the Penguins as a free agent after 10 seasons and was promptly signed to a two-year, $6.3 million contract with the
Seattle Kraken. In the season with the Kraken, Dumoulin notched 6 goals and 10 assists for 16 points in 80 appearances from the blueline. He set a single-season career high in goals to rank third among Kraken defensemen.
Anaheim Ducks With a year remaining on his contract, Dumoulin was traded after just one season with the Kraken to the Anaheim Ducks in exchange for a fourth round pick in
2026 on July 2, 2024.
New Jersey Devils In the final year of his contract with Anaheim, Dumoulin was traded to the
New Jersey Devils on March 6, 2025, in exchange for prospect Herman Träff and a 2025 2nd round draft pick. Dumoulin played out the remainder of the regular season for the playoff bound Devils in a second-pairing role, registering 1 goal and 6 points through 19 appearances. He went scoreless through 5 post-season games in a first-round defeat to the
Carolina Hurricanes.
Los Angeles Kings Having concluded his contract with the Devils, Dumoulin left as a free agent and was signed to a three-year, $12 million contract with the Los Angeles Kings on July 1, 2025. ==Playing style==