Feldon studied acting at
HB Studio. Following working as a model, Feldon's break came in the form of a popular and much-parodied television commercial for "Top Brass," a hair
pomade for men by Revlon. Lounging languidly on an animal-print rug, she purred at the camera, addressing the male viewers who use it as "tigers." This led to small roles in television series. In the 1960s, she made appearances on ''
Twelve O'Clock High (season one episode "End of the Line"), Flipper (season one two-parter episode "The Lady and the Dolphin") and The Man from U.N.C.L.E.'' (in "The Never-Never Affair", which aired spring 1965). In 1964, she appeared with
Simon Oakland in the episode "Try to Find a Spy" of
CBS's short-lived drama
Mr. Broadway. Feldon was cast in this new show as "Agent 99". She starred opposite comedian
Don Adams, who portrayed Maxwell Smart, "Secret Agent 86". The character was unusual for the era, showing a capable woman succeeding in a stressful career. Feldon noted, "A lot of women said 99 was a role model for them because she was smart and always got the right answer." Feldon almost lost her role as 99 because the sponsor of
Get Smart was a deodorant soap, and she had done a deodorant commercial for Revlon. Feldon was also noticeably taller than Adams, her male co-star, another rarity for the time. Feldon reprised her role as "Agent 99" in the made-for-television film
Get Smart, Again! (1989) and in a short-lived revival of
Get Smart in 1995. She wrote and provided audio commentaries and introductions for the DVD release of the original
Get Smart series in 2006, but did not take part in the
2008 film adaptation that starred
Steve Carell as Maxwell Smart. Feldon guest-starred as a former TV spy star on a 1993 season one episode of
Mad About You as Diane "Spy Girl" Caldwell. Feldon played Lauren Hudson, Sam Malone's annual Valentine's Day love interest, in the 1991
Cheers episode "Sam Time Next Year". Feldon's distinctive voice has been heard in numerous TV and radio commercials and film and TV documentaries. She has occasionally acted in off-Broadway plays but said she is "no longer interested in performing". Feldon is an accomplished writer and is still actively writing. In 2015, she had two editorial pieces featured in
Metropolitan Magazine. She wrote two books,
Living Alone and Loving It, in 2003, and
Getting Smarter: A Memoir in 2021. ==Personal life==