The actor, a double Oscar winner, will join Sir Elton's partner David Furnish at his Winter Ball.
Around 600 guests are expected for the event at Battersea Power Station, south London, at the weekend, which will raise money for the Elton John Aids Foundation and feature performances by Emeli Sande and Labrinth.
George cancelled the gigs in September, saying he was wrong to think he could work through the "major anxiety that has plagued" him since his life-threatening battle with pneumonia.
The singer, who nearly died late last year, was due to take his Symphonica tour down under in November and December but in a statement on his website said he had decided he could no longer go through with it.
He said doctors told him he needed "complete rest" and "post-traumatic counselling".
George, 49, began his 64-date tour last year but was forced to pull out when he became dangerously ill after performing in Austria, spending around a month being treated in hospital there.
The Grey Goose Winter Ball to benefit the Elton John Aids Foundation will be held on Saturday November 10.