First recorded by Patti Drew (US #62/R&B #34 1968).
Also recorded by Barbara Lewis (1968), Neil Sedaka (1969).
Other hit version by The 5th Dimension (US #20/R&B #15 1969).
From the wiki: “Neil Sedaka co-wrote ‘Workin’ on a Groovy Thing’ in 1968 but did not record his own version of the song until 1969 when touring Australia. Sedaka recorded an album titled Workin’ on a Groovy Thing on a one-off basis for a Sydney, Australia-based label at a time his career had slumped and his contract had not been renewed by his former label in the USA. (In the United Kingdom, the album was released on the MCA label under the title Sounds of Sedaka.) Patti Drew was the first to record and release the song, in 1968.