Grant appeared as "The Voice" in 2+2+2 at American Nights at The King's Head Theatre, from 3 to 29 July 2007, and in 2008 co-starred in the London-based comedy Filth and Wisdom. On 22 November 2007, he gave a keynote speech at North London Collegiate School in north London as part of their Performing Arts Centre Opening Festival, and presented the 2008 Laurence Olivier Awards.
In 2008, he made his musical theatre debut with Opera Australia, playing the role of Henry Higgins in My Fair Lady, at the Theatre Royal, Sydney, a role he reprised in 2017 at the Lyric Opera of Chicago. In 2009, he played Alain Reille in Yasmina Reza's one-act play God of Carnage at the Theatre Royal, Bath: and subsequently at Cheltenham, Canterbury, Richmond, Brighton and Milton Keynes.
In October 2008, Grant told The Times that he is an atheist. He is an avid supporter of Premier League football club West Ham United. In April 2014, Grant launched his new unisex perfume, JACK, exclusively at Liberty of Regent Street, London. Grant runs the perfume business in collaboration with his daughter.