Miami Heat / Sioux Falls Skyforce (2021–2024)
On September 14, 2021, Martin signed with the Miami Heat on a two-way contract, splitting time with the Sioux Falls Skyforce. He made his Heat debut on October 21, recording five points and two steals in a 137–95 win over the Milwaukee Bucks. On December 8, Martin scored a career-high 28 points, alongside eight rebounds, three assists and two steals, in a 113–104 win over the Bucks. On February 15, 2022, the Heat converted Martin's contract to a standard deal. During the playoffs, the Heat faced the Atlanta Hawks during their first round series. Martin made his playoff debut on April 17, scoring two points in a 115–91 Game 1 win. The Heat reached the Eastern Conference Finals, but were eliminated in seven games by the Boston Celtics.
On July 6, 2022, Martin re-signed with the Heat on a 3-year, $20 million deal. On October 22, 2022, during a 112–109 win over the Toronto Raptors, Martin was ejected after an altercation with Raptors center Christian Koloko. The next day, the NBA suspended Martin for one game without pay due to the altercation.
During the first round of the 2023 NBA playoffs, Martin played a key role in the eight-seed Heat upsetting the top-seeded Milwaukee Bucks, averaging 11.2 points, 5.4 rebounds, and 2 assists per game. On May 19, 2023, Martin scored 25 points during a 111–105 Game 2 Eastern Conference Finals win against the Boston Celtics. In Game 7 of the series, Martin scored 26 points, and grabbed 10 rebounds in a 103–84 win, helping the Heat advance to their second NBA Finals appearance in four years. Martin came one vote short of besting teammate Jimmy Butler for Eastern Conference Finals MVP while averaging 19.3 points and 6.4 rebounds per game, whilst shooting 60.2% from the field and 48.9% from three. Martin struggled in the NBA Finals averaging only 7.4 points on 37.5% shooting. The Heat lost the Finals in 5 games to the Denver Nuggets.
