Written and first recorded (as an instrumental demo) by K.C. & The Sunshine Band (1974).
Hit version by George McCrae (US #1/R&B #1/UK #1/AUS #1 1974).
From the wiki: “‘Rock Your Baby’ was written and produced by Harry Wayne Casey (‘K.C.’) and Richard Finch of K.C. & The Sunshine Band, and is considered to be one of the landmark recordings of early disco music.
“The backing track for the record had been recorded in 45 minutes as a demo, and featured guitarist Jerome Smith, saxophonist Whit Sidener and trumpeter Vinnie Tanno of K.C. & The Sunshine Band. The track was not originally intended for McCrae. But, he happened to be in the studio, was invited by K.C. to add a vocal, and the resulting combination of infectious rhythm and falsetto vocal made it a hit. An instrumental re-recording would later be released as a separate single, in 1975 in the US (backed with ‘S.O.S.’) and in 1976 in the UK (backed with ‘Sunshine City’).
“‘Rock Your Baby’ inspired the drum part in the ABBA hit ‘Dancing Queen’. The chord progression of John Lennon’s #1 single ‘Whatever Gets You thru the Night’, released a few months later, also bears a great resemblance to the one found in ‘Rock Your Baby’. Lennon later admitted to using the song as an inspiration.”
George McCrae, “Rock Your Baby” (1974):