Mitchell was named an alternate captain for the 2018-19 season.[3] He put together another good season, scoring six goals and 21 assists. Despite losing early in the 2019 NCHC Tournament, Mitchell and the Pioneers qualified for the 2019 NCAA tournament, where they put together a run to the Frozen Four before losing to the UMass Minutemen.
Mitchell considered going pro and signing with the Blackhawks prior to the 2019–20 season, but elected to stay with Denver, where he was named captain.[4][5] He had his most successful collegiate season, scoring a career high 10 goals, as well as 22 assists for 32 points. For his efforts, he was named AHCA First-Team All-American.[6] Denver was set to play the Omaha Mavericks in the 2020 NCHC Tournament, but the tournament was canceled before any games were played due to the COVID-19 pandemic. Similarly, the 2020 NCAA tournament was also cancelled.
Professional
Chicago Blackhawks
Mitchell decided to forgo his senior season at Denver, and signed an entry-level contract with the Blackhawks on April 11, 2020.[7][8]
Mitchell made the Blackhawks' opening night roster to start his delayed rookie season.[9] Mitchell logged his first NHL point on January 22, 2021 against the Detroit Red Wings with an assist on a goal by Calvin de Haan. He scored his first NHL goal on February 11, 2021 against the Columbus Blue Jackets. Although not a lineup regular, Mitchell stayed with the NHL club for the majority of his rookie season, finishing with three goals and four assists in 39 games.
In 2021–22 Mitchell did not find the same NHL success that he found in his rookie season, as he spent the majority of the year with the Blackhawks' AHL affiliate, the Rockford IceHogs. In the AHL, he scored 11 goals and 24 assists for 35 points in 57 games. He also played in five playoff games, registering a goal and assist before the IceHogs were eliminated in the second round by the Chicago Wolves. Mitchell played with the NHL club for eight games, registering a lone assist.
Although he started the 2022–23 season with the IceHogs again, Mitchell was called up on November 18, 2022.[10] After that, he served as a reserve body for Chicago's defense, rotating in-and-out of the lineup as needed, but could not lock down a consistent spot in the everyday lineup.[10] He scored a goal and added seven assists in 35 games with the Blackhawks.
Boston Bruins
On June 26, 2023, as an impending RFA, Mitchell was traded by the Blackhawks to the Boston Bruins with Alec Regula in exchange for Taylor Hall and Nick Foligno, reuniting him with his head coach from Denver, Jim Montgomery.[11] Mitchell signed a one-year, two-way contract worth $775,000 with the Bruins on July 10, 2023, avoiding arbitration.[12]
Mitchell won the seventh defensemen job out of training camp for the Bruins, and started the season on the NHL roster.[13] Mitchell scored his first point as a Bruin with an assist on a goal by Matt Poitras against the Anaheim Ducks on October 22, 2023. Mitchell was placed on waivers on October 25, but cleared.[14][15] Mitchell was quickly called back up a few days later, after playing a few games for the Bruins AHL affiliate, the Providence Bruins. However, on December 29, 2023, Mitchell was once again put on waivers, and once again cleared.[16] Mitchell spent the rest of the regular season playing for Providence, helping them to a playoff berth in the 2024 Calder Cup playoffs. In the regular season for Providence, Mitchell provided solid offensive output, scoring six goals and 18 assists in 42 games. In the playoffs, this continued, as he scored two goals and two assists in four games in Providence's first round series against the Hartford Wolf Pack. Unfortunately, this was not enough to overcome the Wolf Pack, as the Bruins were eliminated in four games.
As a pending free agent, Mitchell opted to continue his tenure with the Bruins by signing a one-year, two-way contract extension on June 23, 2024.[17]
