The label of the single gives writing credit simply to "Mar-Keys"; it was registered with BMI as having been written by Charles Axton, Floyd Newman, Gilbert C. Caple, Jerry Lee Smith and Chips Moman.
The song is in a twelve-bar blues form, with brief stops, where Floyd Newman intones "Last Night" before his saxophone solo, which is followed by him exclaiming "Oh, yeah!"
According to Steve Cropper, in an interview with Paul Nassari of the Sunday Mail newspaper, in Adelaide, Australia, "Jerry Lee ‘Smoochy’ Smith came up with the piano riff that was played on organ.
Since [producer Chips] Moman didn't want a guitar on it for whatever reason, I wound up playing the hold-down on the organ on the root note.
"[citation needed] "Last Night" reached #3 Pop and #2 in the R&B charts in the United States.