Preston had been in a coma in Scottsdale, Arizona, since last November after suffering kidney failure, the legacy of a long battle with drugs.
A young keyboards prodigy from Houston, Texas, Preston spent most of his life in the entertainment business. While still a teenager, he played with the likes of Mahalia Jackson, Little Richard and Ray
Charles.
He entered the Beatles' orbit in 1969, as the band was on the verge of breaking up, and helped to soothe some of the tension.
He performed on both sides of the Get Back/Don't Let Me Down single, which was credited to "The Beatles with Billy Preston", the first time the band had shared the spotlight with a sideman. He also accompanied them during their last concert that year, the famous rooftop gig in London.
In the early 1970s, he topped the charts as a solo act with the
Grammy-winning instrumental Outa Space, Will It Go Round in Circles and Nothing From Nothing. He also wrote Joe Cocker's 1974 hit You Are So Beautiful.
At the same time, he was becoming a fixture with the Rolling Stones, recording such tracks as Can't You Hear Me Knocking and Heartbreaker, and playing on several tours.
Born William Everett Preston on September 9, 1946, he moved with his family to Los Angeles when he was two. He was having piano lessons at age three, and performing as a teenager.
He appeared in the 1958 film St Louis Blues, which starred Nat King Cole as bluesman WC Handy. Preston played Handy as a child.
Gospel legend Mahalia Jackson was also in the film, and he would go on to play organ on some of her best-known recordings, including In the Upper Room.
In 1962, Little Richard hired Preston to join his backing band for a European tour. He met the Beatles during their residency at the Star Club in Hamburg, Germany, and also Sam Cooke, who signed him to his SAR label.
After a stint playing in the house band for the TV show Shindig, he joined Ray Charles' band. Beatles guitarist George Harrison renewed their friendship, and brought him into the Apple Studios in January 1969 where the Fab Four were working Let It Be.
His organ handiwork can also be heard on such Beatle songs as
Let It Be, I Want You (She's So Heavy) and Something.
Harrison signed him to Apple Records and co-produced Preston's two albums for the label, That's the Way God Planned It and Encouraging Words.
Preston also contributed to many Beatle solo albums, including Harrison's All Things Must Pass, John Lennon's Sometime in New York City and Ringo Starr's Sentimental Journey.
His credits with the Rolling Stones included the albums Sticky Fingers and Black and Blue. He was a favorite of Mick Jagger, who danced seductively with Preston in the video clip for Hey Negrita. Not only did he tour with the Stones, but he also opened for them.
In his later years, he toured with Eric Clapton and Steve Winwood, as well as Motown session musicians the Funk Brothers. He also was featured on Ray Charles' last album Genius Loves Company, as well as the latest albums by Neil Diamond and the Red Hot Chili Peppers.
Rolling Stones frontman Mick Jagger said in a statement: "Billy was a fantastic and gifted musician a superb singer in both recording sessions and onstage. "He was great fun to be with and I will miss him a lot."
Elton John said: "He was one of my true inspirations, one of the greatest keyboard players of all time and not too shabby a vocalist either."