[4] On November 3, he was acquired by the Sioux Falls Skyforce of the NBA Development League as an affiliate player of the Heat.

[6] Three days later, he made his NBA debut against the Golden State Warriors, appearing for 1:44 minutes and scoring two points on a pair of free throws.

[12] Five days later, he scored 24 points and played in a career-high 44 minutes off the bench as he helped the Heat defeat the Sacramento Kings, 114–109.

[14] On July 9, 2015, Johnson was sidelined for six weeks with a broken jaw that he sustained while playing for the Heat during the 2015 NBA Summer League.

[18][19] After initially trying to avoid surgery, Johnson ultimately gave into the idea on February 1, 2016,[20] a procedure that ruled him out for three months.

He returned to action on May 1, coming off the bench for the final six minutes of the Heat's Game 7 win over the Charlotte Hornets in the first round of the playoffs.

[28][29] Two days later, he scored 18 points against his former team, the Miami Heat, to help the Suns snap a franchise-record 17-game losing streak to win 124–121.

[30] On April 4, 2019, Johnson was ruled out for the rest of the season after missing 10 games with right knee soreness and undergoing arthroscopic surgery.

In the Nets' elimination from the NBA playoffs against the eventual champion Milwaukee Bucks, Johnson totalled 4 points, 2 rebounds, and 5 assists in a combined 22 minutes of action.

[36] Johnson won praise for his personality fit and work with the Nets second unit, but Brooklyn chose not to re-sign him in free agency.