A native of Galveston, TX, who began acting in local and regional theater, Helmond went to New York in the early 1950s and worked with some of the Northeast's most prestigious repertory companies. Helmond owned and operated a summer theater in the Catskills for three seasons and soon established enough of a reputation to win teaching posts in several top university theater programs. She acted steadily on the New York stage, and her portrayal of the tragicomic figure Bananas in "The House of Blue Leaves" won her several awards for both the New York and L.A. productions. In 1973, she received a Tony nomination for her work in a Broadway revival of Eugene O'Neill's "The Great God Brown".

Helmond got her first feature break doing a bit in "Believe in Me" (1971), and supporting roles followed in Robert Wise's docudrama "The Hindenburg" (1975) and in Alfred Hitchcock's final film, "Family Plot" (1976). Terry Gilliam cast her as the Ogre's wife in "Time Bandits" (1981) which led to a featured role in his dazzling look at a bleak future, "Brazil" (1985). Helmond was memorable as the beauty-conscious mother of a ministry chief who, in one bizarre scene, has her face pulled like taffy to get rid of the wrinkles. She was also singled out for her performance as an unpredictable, loony noblewoman in the otherwise unremarkable English comedy "Shadey" (1985).

Helmond has had numerous roles in TV-movies, including a bit in the TV landmark "The Autobiography of Miss Jane Pittman" (CBS 1974). But it was the series "Soap" (ABC, 1977-81) that made Helmond a bonafide TV star. She played the spacey Jessica Tate, the wealthier of two small-town sisters spotlighted by the soap spoof and picked up four Emmy nominations. Helmond was next featured in "Who's The Boss?" (ABC, 1984-92) as Mona Robinson, a liberated grandmother who drops in and out of the day-to-day of her divorced daughter and her live-in male housekeeper. Helmond, who completed the prestigious AFI Director's Workshop for Women, also directed several episodes of the show. In 1995, she joined the cast of the ABC sitcom "Coach" in the recurring role of an eccentric owner of a football team who hired Craig T Nelson's title character.