The singer threw the joint party with artist Sam Taylor-Wood, who is understood to be celebrating her 40th.
The pair are close friends, and Taylor-Wood was one of the few guests at John’s marriage to David Furnish in December 2005.
They have frequently collaborated on fundraising events for the Elton John Aids Foundation.
Stars including Grant, McCartney and actress Thandie Newton were among those arriving for the party at the Shoreditch Town Hall in east London on Tuesday night.
There were also Pearly Kings and Queens.
John and Furnish both donned military garb, while Taylor-Wood wore a floor-length white gown and McCartney arrived in bow tie and tails.
Newlyweds Liz Hurley and Arun Nayer, close friends of the superstar, are still honeymooning after their lavish nuptials and were not at the party. John was a guest of honour at the wedding, walking Hurley down the aisle and singing after the speeches.