The "Heroes" villain will play Daniel Douglas, a charming Southerner with ties to one of the gladiators. Little else is known about his character.
Coleman's recent TV credits include "Burn Notice," "The Vampire Diaries" and ABC's "Castle."
He joins previously announced recurring actors Lisa Kudrow and Paul Adelstein, whose roles are also being kept under wraps by showrunner Shonda Rhimes.
TV Line recently reported that "Army Wives" alum Sally Pressman will also have a multi-episode arc during the upcoming third season. It's not known who she will be playing, but her character is expected to debut in November.
Season 2 of "Scandal" ended as Olivia (Kerry Washington) was no longer able to keep her relationship with President Fitz (Tony Goldwyn) a secret after someone leaked to the press that she is the mistress of the President.
"We start right after Season 2 ended ... and Olivia's just been outed as his [President] mistress so she is no longer the fixer - she is the client," Bellamy Young, who plays the President's wife Mellie, recently told Wetpaint about the upcoming season.
"Mellie is the fixer in her own mind. We're looking at a re-election campaign, so I gotta handle it because we need four more years and Mellie has a very particular idea about who the scapegoat should be, what a strategy should be, how to push it all under the rug so we can get past and get re-elected."
"Scandal" is scheduled to return for Season 3 on Thursday, Oct. 3 at 10/9 p.m. CT on ABC.