Provost was born in Los Angeles. At the age of four, Provost was cast in the film The Country Girl (1954), starring Bing Crosby and Grace Kelly. He then appeared in Back from Eternity (1956) with Anita Ekberg and Escapade in Japan (1957), with Teresa Wright, Cameron Mitchell, and an unknown and uncredited Clint Eastwood.
In 1957, Provost won the role of Timmy Martin in the CBS television series Lassie. He joined the show at the top of the fourth season as co-star to Tommy Rettig, Jan Clayton, and George Cleveland. Midpoint in the season, George Cleveland died and the show was completely revamped with Provost becoming the primary human star after the departures of Rettig and Clayton. The following year, he met June Lockhart on the set, who would play his mother, Ruth Martin, on the set, and would remain close friends. On December 25, 1958, Provost and Lassie were holiday guests on NBC's The Ford Show, Starring Tennessee Ernie Ford.
For seven seasons, 1957–1964, audiences grew to love Timmy and his adventures with Lassie. Timmy's canine companion was played by three dogs that were all descendants of Pal, the original Lassie from the MGM films: Pal's son Lassie Jr. and his grandsons Baby and Spook. In a 2014 interview, Provost said: "I worked with Baby for five years straight. Obviously, he and I really bonded. He was my favorite and I also thought he was the most intelligent of the ones I worked with. They were all great dogs."
In 1964, however, Provost was 14 and chose not to renew his contract though Campbell's Soup Company, the sponsor, wanted three more years.
Provost continued working in television and in films, including "This Property is Condemned" with Natalie Wood and Robert Redford and "The Computer Wore Tennis Shoes" with Kurt Russell. Jon left Hollywood for college at Sonoma State and chose to remain there, returning for occasional roles. Later, he sold real estate in Sonoma County, California and donated his time to various causes.
In 1990, Provost was honored by the Young Artist Foundation with its Former Child Star "Lifetime Achievement" Award for his role as Timmy Martin on the original Lassie series, and in 1989, he returned to television with a recurring role on The New Lassie series as real estate agent Steve McCullough.
He also attends celebrity conventions and autograph shows and works for animal causes.
In 1994, Provost received a star on the Hollywood Walk of Fame at 7080 Hollywood Blvd. His memoirs, Timmy's in the Well: The Jon Provost Story, were released in December 2007 (Cumberland House Publishing, ISBN 1-58182-619-2). In August 2008, Provost was honored with a "Lifetime Achievement Award" at the Pocono Mountains Film Festival.2013: Susie's Hope, as Don Vaughan, a former member of the North Carolina State Senate
1970: The Secret of the Sacred Forest
1969: The Computer Wore Tennis Shoes, starring Kurt Russell
1966: This Property Is Condemned
1964: The Wayfarers (TV)
1964: The Disappearance (TV)
1962: Lassie's Great Adventure (The Odyssey) (TV)
1957: Escapade in Japan
1956: Toward the Unknown
1956: All Mine to Give
1956: Back from Eternity
1954: The Country Girl
1953: So Big