Long will play a recurring role on the Grey's Anatomy spinoff's sixth season, TV Guide reports.
His character is a new doctor who joins the team at St. Ambrose hospital. Long's past credits include short-lived drama series Jack & Bobby and a recent guest spot on HBO's The Newsroom.
Private Practice star Kate Walsh is to depart the medical drama at the conclusion of season six, but the 44-year-old actress has insisted that the series can "absolutely" survive without her.
"The show is so solid - the writing, the characters, the stories," she suggested. "It's got a huge, huge foundation and roots. So yeah, I could absolutely see it going on."
Private Practice returns to ABC on Tuesday, September 25 at 10/9c.
> Private Practice for musical episode?
Watch a clip from the last season of Private Practice below: