In 1965, while attending Baylor, O'Neil performed on two locally produced TV specials, both of them airing on
KCEN-TV. First, on May 14, she was one of 18—and one of three Baylor students—selected to appear on ''Talent '65''. Sponsored by
Southwestern Bell and produced by
KHOU-TV for the purpose of showcasing statewide talent, it was hosted by
John Hambrick. Accompanying herself on guitar, O'Neil performed "
Babe, I'm Gonna Leave You" (
Anne Bredon's composition, popularized in 1962 by
Joan Baez). On December 24 and 25, she and the Baylor University Religious Hour Choir were featured on
Christmas: Old and New, an hour-long special which was heard in
Dallas on
WFAA (AM) on Christmas Eve and seen on KCEN on Christmas Day. Following her graduation from Baylor, O'Neil sang in supper clubs in Texas and California for two years before an opportunity to act on Broadway arose. By that time, O'Neil had already dropped "Patti" in favor of "Tricia", after discovering there was already a Patti O'Neil registered at
Actors Equity. In 1970, O'Neil made her professional theatrical debut in the
Broadway musical
Two by Two. Although the show received mixed reviews, O'Neil earned a
Theatre World Award for her performance.
Newsweek's
Jack Kroll, in particular, singles out O'Neil, amidst his otherwise blistering critique of the show itself: There is only one delight in 'Two by Two'—Tricia O'Neil as Rachel, Noah's daughter-in-law who marries the wrong son. Miss O'Neil is a stunning girl with a full sweet voice and the grace of an Assyrian lioness. She is the only Biblical thing in the show, bearing the wheat of Zion in her hair, the loyalty of Ruth in her eyes, the determination of Judith in her arms, the sensuality of the Song of Solomon in her throat and the curve of her thigh. O'Neil made her film debut in the 1972 film
The Legend of Nigger Charley (1972). Other film appearances include
The Gumball Rally (1976),
Mary Jane Harper Cried Last Night (1977),
Are You in the House Alone? (1978),
The Kid from Left Field (1979),
Brave New World (1980),
Piranha II: The Spawning (1982),
Ted & Venus (1991) and
Titanic (1997). O'Neil made her television debut in the 1973 television movie
Duty Bound. She appeared in a number of guest roles on various television series, including a dog trainer in a 1978 episode of
Columbo titled "How to Dial a Murder", nightclub singer Julie Heller in the episode "Murder! Murder!" of
The Eddie Capra Mysteries (1978), as Dorothy Fulton in
Hart to Hart (1979), as a police photographer in back-to-back episodes of
Barney Miller (1980), as female stunt woman "Charlie" in the episode of the same name in the first season of
The Fall Guy (1981), in
Remington Steele (1982), as conniving "other woman" Ashley Vickers in the pilot episode of
Murder, She Wrote (1984), as a pushy reporter in the second-season episode "Catch of the Day" in
Riptide (1984), as the owner of a travelling Wild West rodeo show in the third-season
Airwolf episode "Annie Oakley" (1985), and separate roles in three episodes of
Matlock from 1989 to 1994. She appeared in the television miniseries ''
Jacqueline Susann's Valley of the Dolls (1981) and in two episodes of The A-Team'', playing Dr. Maggie "Mo" Sullivan in the season one episode "Black Day at Bad Rock" and the season two episode "Deadly Maneuvers". O'Neil guest-starred in the
Babylon 5 season-one episode "
Believers" (1994) as "M'ola". Later, she played the
Earth Alliance president in the
Babylon 5 TV movie
Babylon 5: In the Beginning (1998). In 1991, O'Neil filmed her scenes in the role of Hoelun for the never-released film
Genghis Khan. Efforts in 2010 to repackage the material as a miniseries, tentatively named
Genghis Khan: The Story of a Lifetime, never came to fruition. O'Neil's last screen appearance was on the television series
JAG, playing Dr. Beth Salluci in the 2001 episode "
Redemption". ==Personal life==