They and a host of other stars were on hand to see Moonrise Kingdom, the new film from US director Wes Anderson, launch the annual cinema showcase.
Bruce Willis, Bill Murray and Britain's Tilda Swinton joined other cast members at the movie's glitzy premiere.
The film is one of 22 in contention for Cannes' prestigious Palme d'Or award.
Reactions to Anderson's latest have been broadly positive, with The Guardian's Peter Bradshaw saluting "a soufflé of strangeness [that] rises superbly".
The Telegraph's David Gritten was similarly effusive, describing it as "a mood elevator of a movie" and "an ideal opener" for this year's event.
Moonrise Kingdom was a suitable curtain-raiser for a festival in which US films and directors are heavily represented.
The main competition line-up contains six US-based movies, among them a new thriller starring Brad Pitt and an adaptation of Jack Kerouac's seminal novel On the Road.
"American cinema is back in force," said Cannes' artistic director Thierry Fremaux, when he announced the programme last month.
The US invasion continues on Friday with an out of competition screening of the latest DreamWorks animation, Madagascar 3: Europe's Most Wanted.
Only one British film - The Angel's Share, directed by Ken Loach - is up for the Palme d'Or. Yet British talent is well represented in other areas.
On Thursday the Critic's Week sidebar launches with Broken, a London-based drama from acclaimed theatre director Rufus Norris, starring Tim Roth and Cillian Murphy.