Co-written and first recorded by Garry Bonner (1969).
Also recorded by Spice (1969, released 1974).
Hit version by Three Dog Night (US #15/CAN #8 1970).
From the wiki: “‘Celebrate’ was cowritten by Garry Bonner with Alan Gordon, who also cowrote The Turtles’ ‘Happy Together’ and ‘She’d Rather Be With Me’, and first recorded by Bonner in 1969. It was covered in 1969 by Spice, the immediate precursor to the English band Uriah Heep, but went unreleased until 1994’s The Lansdowne Tapes compilation. In 1970, Three Dog Night recorded ‘Celebrate’ for their Suitable for Framing, and released it as the album’s third single.”