Sayer was born on 21 May 1948 to an Irish mother and English father in Shoreham-by-Sea, Sussex, England. He was initially discovered by musician David Courtney, who then co-managed him with the singer turned manager, Adam Faith.
Sayer began his music career co-writing songs with David Courtney, including "Giving It All Away", which gave Roger Daltrey of The Who his first hit without The Who in 1973.
That same year, Sayer began his career as a recording artist. At the time of his initial chart breakthrough in the UK, with his second single "The Show Must Go On", he wore a pierrot style costume and make-up and the song went quickly to number two. He had several subsequent single hits including, "One Man Band" (1974), "Long Tall Glasses" (1974) and "Moonlighting" (1975). In 1976, Sayer recorded three Beatles songs, "I Am the Walrus", "Let It Be" and "The Long and Winding Road" for the film, All This and World War II.
In 1977, he had a US number one with "You Make Me Feel Like Dancing" (a Grammy Award winner for the year's best Rhythm and Blues Song), as well as the romantic ballad, "When I Need You" (1977), which reached number one in both the UK and US. Written by Albert Hammond and Carole Bayer Sager, it was Sayer's first UK chart-topper (after three number two hits) and his second successive US number one. It was also the first of two UK chart-toppers in a row for producer Richard Perry.
Sayer also made cover versions of Bobby Vee's Sonny Curtis/Jerry Allison composition, "More Than I Can Say" (his fourth UK number 2 hit and US number 2), and Buddy Holly's "Raining in My Heart" (1979) and "Orchard Road" in 1983. In the US, three of his singles - "You Make Me Feel Like Dancing" (1977), "When I Need You" (1977) and "More Than I Can Say" (1980) - were certified gold.
In 1978, Sayer made an appearance on The Muppet Show. Sayer also provided songs for the soundtrack of the French-Belgian animated film, Le Chainon manquant in 1980. In 1981 he was the voice of Dan the forest ranger in The Raccoons on Ice, the second of four specials serving as a predecessor to the Canadian animated series, The Raccoons. He also sang several songs for the special, all of which were included on the 1983 album Lake Freeze.
In 1990, he contributed to the last studio collaboration between Alan Parsons and Eric Woolfson, Woolfson's solo album Freudiana, performing "I Am A Mirror".
Sayer performed at the Sanremo Music Festival in 1990, with "The Moth And The Flame" (English version of "Tu... sì" by Mango) and, in 1991, with "All Alone" (English version of "Dubbi No" by Mietta).
In 2000, "You Make Me Feel Like Dancing" was featured in the hit film, Charlie's Angels, and was on the accompanying soundtrack album.
On 12 February 2006, he made a surprise return to number one in the UK Singles Chart, with Meck's remix of "Thunder In My Heart". It was his first appearance in the UK Top 10 for
almost 24 years, and his second UK chart-topper, almost three decades after his first. In 2008 Sayer released a new album in Australia, Don't Wait Until Tomorrow. This album, produced by Garth Porter (from the Australian pop band Sherbet), and released by Universal Music Australia, featured selections from his catalog in an entirely new setting, re-arranged with strings and acoustic and jazz instrumentation. Sayer has appeared in various TV shows including The Muppet Show (on which he sang "You Make Me Feel Like Dancing", "The Show Must Go On", and "When I Need You"), The Wiggles 2008 DVD, You Make Me Feel Like Dancing which featured Sayer's hit of the same name, Celebrity Big Brother UK in 2007 and the Australian television comedy, Stupid, Stupid Man.
Leo Sayer: At His Very Best, a career-spanning compilation album, was released in the UK on 6 March 2006. It featured the Meck single, alongside "When I Need You" and "You Make Me Feel Like Dancing".
In January 1967, while 19-year old Sayer was working as a hall porter at the King's Hotel in Hove, he assisted in the rescue of guests from a fire that damaged the first floor of the hotel. He was rescued by builders working on a block of flats beside the hotel. In 2005, Sayer moved to Sydney, Australia, where he has remained. He became an Australian citizen on 26 January 2009 at a naturalization ceremony attended by Prime Minister Kevin Rudd.