Henderson Mullin became active in various black cultural and literary associations while studying Politics at university. He was a founder member of The Rhythm Writers, a performance- based collective in London. He worked in commercial publishing for many years before joining Index On Censorship, the international magazine for free expression, in 1998; he became its publisher the following year. Index regularly features new writers on cultural and political issues alongside the likes of Vaclav Havel, Nadine Gordimer, Salman Rushdie, Philip Pullman, John Le Carré, Günter Grass, Umberto Eco, Jack Mapanje, Aung San Suu Kyi and others.