The team announced just before Friday’s game with Sacramento that they have signed 6-foot-6 swingman to a multi-year contract.
Johnson 23, has appeared in eight games for the Celtics  and has averaged 7.6 points, 2.8 rebounds, and 1.3 assists in 21.6 minutes in eight games. He posted a career-high 12 points against Brooklyn on Jan. 26 and recorded a career-high four steals against Washington on Jan. 22.
Johnson had appeared in 20 games for the Rio Grande Valley Vipers of the NBA Development League earlier this season where he had averaged 19.4 points, 6.8 rebounds, 2.5 assists, 1.6 steals and 1.0 block in 37.2 minutes per game.
According to Chris Forsberg of ESPNBoston.com, Johnson will be paid at a prorated rate based on a salary of $320,000 this season, allowing the Celtics to stay below the luxury tax threshold.
adding Chris Johnson 's pro-rated salary ($320K), C's now at roughly $70.94 million in luxury tax calculations, about $810K shy of line.
— Chris Forsberg (@ESPNForsberg) February 8, 2014