She often performs at The Comedy Store in Los Angeles and was featured as a new face at last year's Just for Laughs Festival in Montreal.
Johnson has featured in many past and recent short films and shows including the Netflix series "Space Force" and HBO's comedy series "A Black Lady Sketch Show".
Although she is the first out Black lesbian SNL cast member, she is not the first overall.
Danitra Vance, who was on the show in 1985 and 1986, has that distinction, though she was not out publicly at the time.
While Kate McKinnon is recognised as the sketch show's first out lesbian cast member, Denny Dillon, who was on the show for one season in the early '80s, was actually the first overall, though she did not come out publicly until later.
Two new cast members will also join Johnson, Lauren Holt, an actor, comedian, singer and improviser, and Andrew Dismukes, who has been an "SNL" staff writer since season 43.
