Mary Klug is an actress, best known for Black Mass, The Box, The Invention of Lying, and The Departed. Other film credits include Clear History, Brotherhood, Easy Listening, and Housesitter.

Theatre credits include Stella Livingston in Light Up The Sky (Lyric Stage); Cashier in These Are the Stairs You Got to Watch and Watch/Anna in Summer at the Lake (SpeakEasy Stage); Mrs. Grant in The Front Page, Sister Clarissa in Over the Tavern, Cookie Cusack in Rumors, Marina in Uncle Vanya, Mrs. Wilson in Lovers, and Rosalia in Filumena (Merrimack Repertory); and Fonsia Dorsey in The Gin Game (New Repertory).