Nussbaum will join WWF-UK later this month. He is currently chief executive of Berlin-based anti-corruption organisation Transparency International, where he has worked for four years. He was finance director of Oxfam between 1997 and 2003.
"WWF is well placed to engage with globalisation and the growing significance of all kinds of international interactions," said Nussbaum. "In the UK, it has an influential role to play in its relationships with government, companies and citizens."
He succeeds Robert Napier, who retires after eight years at the helm and will concentrate on his role as chairman of the Met Office.