The Justified actor will star in at least two episodes of the comedy, TV Guide reports.
Paul Lieberstein, who plays Toby as well as writing and producing the show, explained that Olyphant's character will be a new enemy of Michael's.
"He steals clients away from Jim and Michael and Dwight, so they have a little sting set up," Lieberstein said. "They set up a fake company to see what his secret is."
The Office returns for a new season on September 23 on NBC.