In September 1967 at the age of 18, he was signed to a recording contract and in December of that year released the novelty single "Sadie the Cleaning Lady," which became the biggest-selling single in Australia at that time. As a song, the record's success almost defies logic. What fans were responding to was "Johnny" Farnham's bright boy-next-door personality. He was someone both teenage girls and their mothers could both like. Farnham was also a fine singer and survived "Sadie" to release a long string of pop hits between 1967 and 1973, including the local hit versions of Three Dog Night's "One," B.J. Thomas' "Raindrops Keep Falling on My Head" (number one), and David Cassidy's "Rock Me Baby. He also starred in the stage musicals Dick Whittington & His Cat, Charlie Girl, and Pippin. His schedule prevented Farnham trying his luck internationally or developing on record. Success continued on the basis of his talent his personality, but by the late to mid-'70s, his career was reduced to night club and cabaret performances trading on his past. Even his record company lost faith in him and dropped him.

In 1980, changing from "Johnny" to the more mature John Farnham, he set about resurrecting his career. The trigger was a dramatically rearranged, impassioned performance of the Beatles' "Help" on a nationally broadcast Royal Command TV concert. He reminded everyone what a fine singer he was, and in July, he released Uncovered, a well-received comeback album recorded under the production eye of Little River Band's Graham Goble. In September 1982, longtime Farnham fan Goble was inspired to convince the rest of LRB they should take the radical move of removing Glenn Shorrock, singer of all the band's hits, and making Farnham their lead singer. The band's American record company was in shock. So were non-Australian fans. It was a hurdle Farnham could not overcome, and at the end of 1985, he left LRB and began work on a new make-or-break solo album.

The anthemic single "You're the Voice restored Farnham to number one for the first time in 17 years. The carefully crafted adult contemporary October 1986 album Whispering Jack was number one 18 weeks, and became the biggest-selling album in Australian history. "You're the Voice" sold a million copies in Europe and reached the Top Ten in England. A consummate singer and performer since 1986, Farnham has been Australia's number one attraction, with successive big-selling albums and sold-out concert tours. International interest has continued to beckon, but the dedicated family man is happy with his career as it is.