Dallas Stars

After signing his contract with the Stars, he was reassigned to their American Hockey League (AHL) affiliate, the Texas Stars, for the remainder of the 2010–11 season.^[8] He played 10 games for the team, accumulating no points and eight penalty minutes.^[1] He was invited to the Dallas Stars' training camp prior to the 2011–12 season but was reassigned to Texas on September 28.^[9] After playing 31 games for Texas and recording two goals and 11 assists, Dillon was called up to the NHL level to replace an injured Sheldon Souray.^[10] He saw no action during his recall and was subsequently reassigned back to Texas. Dillon was called up again for the Dallas Stars' last game of the season and made his NHL debut on April 8, 2012, against the St. Louis Blues. He played in 19:59 of ice time and had a game-high six shots on goal, tied for a game-high four hits and co-led the Stars with three blocked shots.^[11] Dillon ended the season with the Texas Stars, tied with Jordie Benn for most assists amongst team defencemen, as the Stars failed to qualify for the Calder Cup playoffs.^[12]

Due to the 2012–13 NHL lockout, Dillon began the season with the Texas Stars before joining Dallas once an agreement was reached.^[12] On February 1, 2013, Dillon registered his first career Gordie Howe hat trick, meaning he recorded a fight, assist, and goal. During that game, he also registered his first career assist and goal in a 4–3 shootout win against the Phoenix Coyotes.^[13] Dillon was also selected for his first international appearance with Canada in the 2013 IIHF World Championship.^[14] He scored one goal in eight games as Canada would lose in the quarterfinal to the eventual tournament champions Sweden.^[12]

The following season, Dillon spent his entire 2013–14 campaign with the Stars and set new career highs. He finished the season with 17 points in 80 regular seasons games and his plus-minus rating ranked fourth amongst all NHL defencemen.^[15] The two games he missed during the season was due to a lower-body injury.^[16] On October 2, 2014, Dillon signed a one-year contract extension to remain with the Stars through the 2014–15 season.^[15] Since his rookie season, Dillon was paired with Stephane Robidas on the left side but, once the player was traded to the Anaheim Ducks, Dillon was moved to the right side.^[17]

San Jose Sharks

On November 21, 2014, Dillon was traded to the San Jose Sharks in exchange for defenceman Jason Demers and a third-round pick in the 2016 NHL Entry Draft. At the time of the trade, Dillon had recorded three assists in 20 games.^[18] Upon joining the team, Dillon was paired with veteran Brent Burns and returned to his natural playing side.^[17][19] Dillon finished the 2014–15 season with the Sharks, recording two goals and seven assists in 60 games. On June 29, 2015, as pending restricted free agent, Dillon signed a five-year, $16.35 million contract extension with San Jose worth an average annual value of $3.27 million per season through to the end of the 2019–20 season.^[20] In the first year of his new contract, Dillon recorded 11 points in 79 games.^[1]

In his third full season with the Sharks, Dillon broke out offensively and set new career-highs in assists and points.^[21] On December 5, 2017, the NHL Department of Player Safety announced that Dillon was suspended one game for slashing Washington Capitals Madison Bowey.^[22]

Following the 2018–19 season, Dillon was the recipient of the Sharks' inaugural "Media Good Guy" Award as "a player who handles his media responsibilities with cooperation, honesty, and thoughtfulness, and answers the bell no matter the outcome or situation."^[23] He was also the Sharks' nominee for the King Clancy Memorial Trophy as a "National Hockey League player who best exemplifies leadership qualities on and off the ice and who has made a significant humanitarian contribution to his community." His nomination was based on his activism with the Sharks Foundation's Stick To Fitness program and the Sharks Foundation's Blacktop Resurfacing projects.^[24]

Washington Capitals

Following the 2019–20 season, with the Sharks out of playoff contention and playing in the final season of his contract, Dillon was traded to the Washington Capitals in exchange for a 2020 second-round pick and a 2021 conditional third-round pick on February 18, 2020.^[25] Upon leaving the Sharks, Dillon ranked ninth in most games in Sharks history and seventh with the most penalty minutes in franchise history.^[26] Prior to the trade, Dillon spoke highly of San Jose and emphasized his wish to remain with the team.^[27]

On October 6, 2020, Dillon opted to forgo free agency and signed a four-year, $15.6 million contract with the Capitals.^[28]

Winnipeg Jets

On July 26, 2021, Dillon was traded by the Capitals to the Winnipeg Jets in exchange for second-round picks in 2022 and 2023.^[29] Later, on December 17, 2021, in his first game against the Capitals since the trade, Dillon scored his first goal as a Winnipeg Jet against his former team.^[30]

On May 1, 2022 Dillon was awarded the Dan Snyder Memorial Award, which exemplifies the player who most embodies perseverance, dedication and hard work. In the 2021-2022 season he finished 1st on the Jets in blocked shots, 1st in fighting majors, 2nd in hits, 2nd in plus minus and for the 3rd time in his career hit the 20 point mark.