Written by real-life couple Nickolas Ashford & Valerie Simpson, it became one of the few Motown recordings of the 1960s that was not recorded with the familiar "Motown sound". Instead, "You're All I Need to Get By" had a more soulful and gospel-oriented theme surrounding it, that was influenced by the writers, who also sing background vocals on the recording, sharing vocals in a church choir in New York City. The lead vocals were recorded separately by the two singers and combined during the mixing process, reportedly to cut studio time, and give time for Terrell, who was using a wheelchair, to recover from surgery on the malignant brain tumor that would ultimately cause her death in 1970.

The original recording by Gaye and Terrell peaked at number seven on the Billboard Hot 100 and number-one on Billboard's Hot R&B/Soul Singles chart for five weeks, becoming one of the longest-running number one R&B hits of 1968 and the most successful duet recording of Marvin Gaye's entire career. Given its global appeal, it also reached #19 on the British singles charts in late 1968, staying there for nineteen weeks.

Dionne Warwick recorded this song in 1969 for the album Soulful and Diana Ross recorded it for her 1970 album, Diana Ross. Ashford and Simpson produced Ross' version as well.

...
Wikipedia