Cartwright was born in Bristol and grew up in Los Angeles, having emigrated to America shortly after the birth of her younger sister, actress Angela Cartwright. Her career as a child actress began in 1958 with a role in In Love and War. Among her early appearances were repeated roles in the television series Leave It to Beaver (as Beaver's classmates Violet Rutherford and, later, Peggy MacIntosh) and episodes of One Step Beyond "The Haunting" (1960) and The Twilight Zone "I Sing the Body Electric" (1962). She guest starred twice in 1963 in NBC's medical drama about psychiatry, The Eleventh Hour, in the episodes "The Silence of Good Men" and "My Name is Judith, I'm Lost, You See." Cartwright appeared in the films The Children's Hour (1961) and Alfred Hitchcock's The Birds (1963), which were both highly successful. In The Birds, she was cast along with her TV father from Leave It To Beaver, Richard Deacon, although the two were not on screen together. She played daughter Jemima Boone in the first two seasons of NBC's Daniel Boone from 1964 until 1966, with co-stars Fess Parker, Patricia Blair, Darby Hinton, Ed Ames, and Dallas McKennon. She won a regional Emmy for the 1964 TV movie Tell Me Not in Mournful Numbers.
Cartwright achieved successes with Invasion of the Body Snatchers (1978) and Alien (1979), the latter performance winning her a Saturn Award for Best Supporting Actress. She was originally cast as Alien's heroine Ellen Ripley, but director Ridley Scott switched her role with Sigourney Weaver's just prior to shooting the film.
Other film roles include: Spencer's Mountain with Henry Fonda and Kym Karath (1963), Inserts (1974), Goin' South (1978), The Right Stuff (1983), Flight of the Navigator (1986), The Witches of Eastwick (1987), Money Talks (1997), Scary Movie 2 (2001), Kinsey (2004) and Straight-Jacket (2004).
A frequent performer in television, she has played guest roles in such series as The Mod Squad, Miami Vice, Baywatch, L.A. Law, ER, The X-Files, Chicago Hope, Will & Grace, Touched by an Angel, Judging Amy, Six Feet Under, The Closer, and Law & Order: Special Victims Unit. Cartwright has received three Emmy Award nominations, one for her work in ER in 1997, and two for her work on The X-Files in 1998 and 1999. Veronica Cartwright also starred as Mrs. Olive Osmond in the made-for-TV film Inside the Osmonds.
She co-starred in the fourth version of Invasion of the Body Snatchers, The Invasion (2007). She appears on the cover art for the Scissor Sisters' 2006 single "I Don't Feel Like Dancin'" as well as on their second album Ta-Dah.
In 2014, Cartwright reprised her role as Joan Lambert for DLC episodes in Alien: Isolation based on the original film, and appeared in the remake of The Town That Dreaded Sundown.
Cartwright is the older sister of actress Angela Cartwright, who appeared in The Sound of Music (1965) and as a regular in the television series Lost in Space and Make Room for Daddy.