Johnson started in film doing special effects, including David Cronenberg's The Dead Zone. This behind-the-scenes work often served as a "backup" for him during the early stages of his acting career.
In 1993, Johnson became part of the original cast of the television series Homicide: Life on the Street playing Detective Meldrick Lewis for all seven seasons and the reunion movie, as well as directing several episodes. Johnson regularly improvised during filming and made up his own jokes and dialogue; writer and producer James Yoshimura called Clark the "king of the ad lib".[4] Although the ensemble nature of the show meant that Johnson never played a minor role, he became an even larger presence after his character was paired with a new partner, Mike Kellerman (played by Reed Diamond). The two detectives became the central figures in a plot line surrounding a Baltimore drug lord whose financial resources and front as a devoted community servant make it nearly impossible for the police department to charge him. Johnson made the transition to director with the season four episode "Map of the Heart".[5][6] He also directed "Betrayal",[7] "Valentine's Day",[8] "Full Court Press"[9] and "The Twenty Percent Solution".[10]David Simon, the author of the non-fiction book Homicide was based upon, as well as a writer and producer for the series, commented that the transition from actor to director was made easy by Johnson's familiarity with the show and that he was one of the better directors in terms of keeping the tone of the show consistent.[6] In 2013, Johnson made a brief cameo as Lewis in the Law & Order: Special Victims Unit episode "Wonderland Story" when the squad are at a retirement party for John Munch (Richard Belzer).
In 2013, Johnson starred as Sen. Robert Bettencourt (R-PA) in Amazon's Alpha House, a political comedy written by Doonesbury creator Garry Trudeau.[16] Along with John Goodman, Johnson plays one of four Republican senators living together in a house on Capitol Hill. Johnson also directed the season finale for the show's first season.[17] Johnson spent the summer of 2014 filming season two.
Johnson's other directing credits include the big-screen releases The Sentinel (2006) and S.W.A.T. (2003), and episodes of Third Watch as well as the HBO original production Boycott (2001), a project which he helmed and in which he also acted. He also directed the first episodes of Seasons 1 and 2 of the 2005 mini-series Sleeper Cell. He also directed the first and last episodes of The Shield, along with other episodes of that series.
Johnson directed the pilot episode of the FX drama Lights Out. The series stars fellow The Wire cast members Pablo Schreiber and Reg E. Cathey and focuses on a retired heavyweight boxing champion.
^Clark Johnson (director), James Yoshimura, Michael Whaley (writers) (April 26, 1996). "Map of the Heart". Homicide: Life on the Street. Season 4. Episode 19. NBC.
^ abDavid Simon (1998). Homicide: Life on the Street Season 4 interviews (DVD). NBC.
^Clark Johnson (director), Tom Fontana, Julie Martin, Gay Walch (writers) (January 10, 1997). "Betrayal". Homicide: Life on the Street. Season 5. Episode 12. NBC.
^Clark Johnson (director), Tom Fontana (writer) (February 14, 1997). "Valentine's Day". Homicide: Life on the Street. Season 5. Episode 16. NBC.
^Clark Johnson (director), David Simon, Philip B. Epstein (writers) (April 3, 1998). "Full Court Press". Homicide: Life on the Street. Season 6. Episode 18. NBC.
^Clark Johnson (director), David Simon (writer) (October 30, 1998). "The Twenty Percent Solution". Homicide: Life on the Street. Season 7. Episode 04. NBC.
