According to The Hollywood Reporter, Harris also has been added to the cast of CBS Films' untitled Crowley project for director Tom Vaughan.
In a 10-episode arc on the acclaimed period drama Mad Men, set at the 1960s-era Sterling Cooper Advertising Agency, Harris will play Lane Pryce, the agency's financial officer.
Harris begins filming today on the Lionsgate TV-produced series, which began production on its new season Monday for an August premiere. He joins returning cast members Jon Hamm, Elisabeth Moss, Vincent Kartheiser, January Jones and Christina Hendricks and guest star John Slattery.
In the Crowley project, a medical drama starring Harrison Ford and Brendan Fraser, Harris will play a biotech executive who oversees Stonehill (Ford) and John's (Fraser) efforts to find a cure for John's children.
He begins filming on Thursday, juggling the movie and Mad Men.