Eileen Brennan (born September 3, 1932) is an American actress of film, television, and theater.

Brennan was born as Verla Eileen Regina Brennen in Los Angeles, California, daughter of Regina "Jeanne" Menehan, a silent film actress, and John Gerald Brennen, a doctor. Of Irish descent, she was raised Roman Catholic.

Eileen Brennan appeared in plays with the Mask and Bauble Society at Georgetown University in Washington, DC, where she was employed. She starred there in Arsenic and Old Lace. Her exceptional comic skills and romantic soprano voice propelled her from unknown to star in the title role of Rick Besoyan's off-Broadway tongue-in-cheek musical/operetta Little Mary Sunshine (1959) and its un-official sequel, The Student Gypsy (1963). She went on to create the role of Irene Malloy in the original Broadway production of Hello, Dolly! (1964). Her feature film debut was in Divorce American Style (1967). She soon became one of the most recognizable (if unidentifiable) supporting actresses in film and television. Her roles were usually sympathetic characters, though she has played a variety of other character types, including earthy, vulgar and sassy, but occasionally "with a heart of gold." A year after her feature film debut she became a semi-regular on the comedy-variety show Rowan & Martin's Laugh-In, but stayed for only two months.