McLachlan has appeared on and off-Broadway in several plays, including the 1992 Broadway premiere of Tom Stoppard's The Real Inspector Hound (as the titular inspector), William Shakespeare, and the 1988 revival of Our Town (with William H. Macy). Films include Magnolia (as one of the historical murderers in the opening), Instinct, The Kid, and National Treasure. On TV, he appeared in episodes of Glee, Veep, House of Lies, Modern Family, Spin City, Law & Order, Boston Legal, ER, and Mad Men.