He is known for his roles as Detective Curtis Lemansky in The Shield, Butch "Burner" Barnes in Pensacola: Wings of Gold, Detective Ham Dewey in Saving Grace, Herman Kozik in Sons of Anarchy, Matt Webb in Prime Suspect, Caleb Calhoun in Bates Motel, Dominique Luca in the CBS drama series S.W.A.T., and Tommy Welch on Chicago Fire (2014–2015).

[2] This path led to him living for a year in Boston, Massachusetts, before finally settling in Los Angeles, California, where he eventually found acting.

A former champion arm wrestler, he appeared as bit characters in various television programs, such as Family Matters, Grace Under Fire, Caroline in the City, Pensacola: Wings of Gold, Sliders, 18 Wheels of Justice, Just Shoot Me!, NCIS: Los Angeles, Lie to Me, Law & Order: Special Victims Unit and The Protector.

Johnson originally auditioned for the role of ill-fated Terry Crowley in The Shield, which ultimately went to Reed Diamond.

[4] After The Shield, Johnson had recurring roles in Cold Case, first as a supposed murder victim and later as a love interest for Lilly Rush.

Johnson also appeared as a regular in NBC's crime drama series Prime Suspect, playing the contractor boyfriend of the lead character, Detective Jane Timoney (Maria Bello).

[5] Also in 2011, Johnson starred as Frank Connor, a convicted drug smuggler who leaves prison after 22 years for one youthful mistake, in Few Options.

[9] He was then a recurring cast member in the fifth season of Covert Affairs, playing former CIA paramilitary operative James Decker.

In August 2015, it was reported that Johnson would be part of the main cast for the second season of ABC's anthology series Secrets and Lies.