The actress was pictured as the 20th century pin-up for the first time at the Cannes Film Festival this week and she has captured the sultry eyes and pout uncannily.
Based on a novel, the film - called Blonde - tells the story of Monroe's tempestuous and ultimately tragic life, as well as her much-publicised romances.
Some critics are saying that Watts is too skinny to play curvy Monroe, but we reckon this is a little unfair - after all, the actress was hardly obese herself and was actually a lot smaller than many people think!
The film doesn't start production until summer next year, so there's plenty of time to get used to the idea anyway.
Yesterday we reported that Paris Hilton had also recently donned a Marilyn Wig in order to promote her new perfume Tease.