He moves after the failure of the specialist retail agency Result, which he set up with the former Comet marketer Alasdair Hirst in 2002. Although the agency won a brief to help the supermarket chain William Morrison to expand into the south and London, Tiratelli and Hirst's partnership has since foundered.
At JWT, Tiratelli replaces Simon Taylor, who moved to JWT's new specialist agency, High Street, as a managing partner. Tiratelli will manage a team of up to 20 account handlers in the UK as well as co-ordinating the network on the account on a global level.
The JWT chief executive, Simon Bolton, said: "Stef comes with a fantastic advocacy from some of his previous clients and his strength in dealing with them on a global level makes him the perfect man for this job. He is also associated with brilliant creative work, which is also crucial when dealing with a client such as Shell."
Tiratelli has a wealth of experience dealing with global clients from his days both at Bartle Bogle Hegarty and Saatchis, where he ran Toyota and Telewest. He left Saatchis in 2001 as part of a restructure implemented by the incoming chief executive, James Hall.
Most recently, he has been working on a freelance basis for agencies such as Abbott Mead Vickers BBDO and Ogilvy & Mather, specifically on new business. He also worked at JWT as a freelance before taking the new role.