Lynagh and Greenwood will help to highlight Heineken's association with the Rugby World Cup, which kicks off in Paris in September. The pair will also drive media partnerships and events.
Jon Lane, Heineken UK's sponsorship manager, said: "We are very excited about the prospect of working with two former world cup winners in the build up to and playing of the Rugby World Cup 2007.
"Both Will and Michael are highly regarded as past players and current pundits of the game and appeal internationally to both fans and the rugby community."
Lynagh was capped 72 times for Australia from 1984 to 1995, playing as captain from 1993 to 1995. After retiring from a 12-year international career, Lynagh played in the Premiership before becoming a TV analyst for Sky Sports.
Greenwood made his international debut in 1997 and amassed 55 caps. He is now a columnist for the Daily Telegraph and pundit on Sky Sports.