St. Louis Blues (2015–2019)

Edmundson began his professional career with the Blues' American Hockey League (AHL) affiliate, the Chicago Wolves, after being cut from training camp.^[23] He recorded his first career goal professional goal on November 13, 2013, in a 3–1 win over the Iowa Wild. His goal came during the second period and proved to be the game winner as the Wolves retook the lead.^[24] Edmundson and the Wolves finished first in the Midwest Division and qualified for the 2014 Calder Cup playoffs where they lost in the second round.^[14] Edmundson was reassigned to the Wolves out of the Blues' 2014 Training Camp^[25] but made his season debut on February 3, 2015, due to an injury.^[26] In 30 regular season games, Edmundson recorded 12 points and 49 penalty minutes as the team finished third in the Midwest Division.^[14]

After playing two seasons with the Wolves, Edmundson made the opening night roster of the St. Louis Blues for the 2015–16 season.^[27] Alongside fellow rookie Colton Parayko, he made his NHL debut on October 8, 2015, against the Edmonton Oilers.^[28] Edmundson alternated between the AHL and NHL throughout the season, playing with the Blues for 23 games before being re-assigned to the Chicago Wolves.^[29] He returned to the NHL roster before Christmas^[29] and scored his first career NHL goal on March 25, 2016, in a 4–0 win over the Vancouver Canucks to help the Blues clinch a playoff spot.^[30] At the conclusion of the season, Edmundson recorded nine points in 66 games and set a franchise record for most hits by a rookie with 162. On April 8, 2016, he signed a two-year contract extension to stay with the Blues.^[31]

Edmundson once again made the Blues opening night roster prior to the 2016–17 season.^[32] His time in the lineup was short-lived as he endured an upper-body injury during a win over the Colorado Avalanche and was placed on injured reserve.^[33] He eventually returned to the Blues' lineup on December 5 after missing 12 games.^[34] Edmundson ended the season with 16 points in 69 games^[1] and was placed on the team's protected list leading up to the 2017 NHL Expansion Draft.^[35]

Entering the second year of his newest contract, Edmundson again made the Blues opening night roster prior to the 2017–18 season.^[36] He was once again alternated in and out of the Blues' lineup due to various injuries throughout the season. On February 9, 2018, Edmundson was placed on the Blues' injured reserve for an expected period of six weeks to recover from a broken right forearm.^[37] After missing 13 games, Edmundson returned to the Blues' lineup on March 15, 2018, and scored in their 4–1 loss to the Avalanche.^[38] Playing primarily with either Alex Pietrangelo or Colton Parayko, Edmundson finished the season with a career high 17 points in 69 games.^[39]

During the 2018 off-season, Edmundson volunteered as a guest instructor at Micheal Ferland's Hockey School in Brandon, Manitoba, alongside Brigette Lacquette, Harley Garrioch, Jens Meilleur, Ryan Pulock, Tyler Plante, Shaq Merasty, Josh Elmes, and Zach Whitecloud.^[40] As a result of his success on the team, Edmundson and Blues agreed on a one year, $3 million contract for the 2018–19 season on July 24, 2018.^[41] He once again began the season with the Blues but suffered a groin injury which delayed his season debut until October 11.^[42] Upon returning to the Blues' lineup, he suffered another lower-body injury during a game against the Arizona Coyotes on March 12, 2019.^[43] Edmundson helped the Blues qualify for the 2019 Stanley Cup Finals against the Boston Bruins, and played in five out of the seven games of the series, to help the Blues clinch their first Stanley Cup in franchise history.^[44] During his Day with the Cup, Edmundson returned to his hometown of Brandon, Manitoba and brought the cup to his training gym, the Sportsplex, and the Western Manitoba Cancer Centre.^[45] As a restricted free agent in the off-season, Edmundson filed for salary arbitration and was awarded a one-year, $3.1 million contract to remain with the Blues.^[46]

Carolina Hurricanes (2019–2020)

On September 24, 2019, Edmundson was traded, along with Dominik Bokk and a seventh-round pick in 2021, to the Carolina Hurricanes in exchange for Justin Faulk and a fifth-round pick in 2020.^[47] He found out about the trade at noon and arrived in Carolina the following morning where he participated in morning practice.^[48] After going pointless in 17 games, Edmundson recorded his first goal as a Hurricane and two assists during a 8–2 win over the Ottawa Senators on November 11, 2019.^[49] By January 19, 2020, Edmundson recorded his 12th point of the season, surpassing his previous seasons point total of 11.^[50] Two months later, Edmundson recorded his 19th point of the season, setting a new career-high in points.^{[citation needed]}

Montreal Canadiens (2020–2023)

On September 12, 2020, Edmundson (a pending unrestricted free agent) was traded to the Montreal Canadiens in exchange for a 2020 fifth-round pick.^[51] On September 16, Edmundson signed a four-year, $14 million contract with the Canadiens.^[52] He noted that his father was a lifelong fan of the team, and thus pleased by this outcome.^[53] Edmundson quickly became an important part of the team's defence, playing most of the 2020–21 season partnered with Jeff Petry.^[54] With the Canadiens making a deep playoff run, Edmundson participated in his second Stanley Cup Finals. The Canadiens were defeated by the Tampa Bay Lightning in five games.^[53]

Upon arrival at the Canadiens' training camp in the leadup to the 2021–22 season, Edmundson was reported as having an undisclosed injury that would keep him from skating with the team, which was later indicated to be a back injury.^[55] It was subsequently announced that he would miss two to three weeks at the beginning of the season.^[56] However, his recovery process was far more protracted, due to multiple setbacks and time away from the team to care for his ailing father. Eventually it was concluded he would not require surgery and returned to practices with the team at the end of February 2022.^[55] Edmundson returned to the ice on March 12, 2022 when the Canadiens hosted the expansion Seattle Kraken for the first time in their history.^[57]

Edmundson was considered a candidate to succeed Shea Weber as the Canadiens' captain in advance of the 2022–23 season, but was instead named an alternate captain while the captaincy was given to Nick Suzuki.^[58] Days later, Edmundson and Suzuki collided while in a training scrimmage, both sustained injuries; in Edmundson's case, the aggravation of his prior back injury put him out indefinitely.^[59] With the team undergoing a rebuild, there was discussion upon his return to the lineup that Edmundson might be traded in advance of the 2023 playoffs trade deadline.^[60] However, this was hindered by Edmundson being injured weeks before the deadline and being kept out of games for that span.^[61]

Washington Capitals (2023–2024)

On July 1, 2023, Edmundson was traded by the Canadiens to the Washington Capitals in exchange for a third and seventh-round pick in 2024.^[62]

Toronto Maple Leafs (2024–present)

On March 7, 2024, Edmundson was traded to the Toronto Maple Leafs in exchange for draft picks.^[63]