Magnolia would appear to be a logical and convenient outlet given that the film was co-produced by 2929 Productions, its sister company in the Wagner/Cuban Companies fold, and had struggled to find a buyer since January.
Former New Line marketing chief Russell Schwartz has been brought on to develop and implement the marketing and distribution strategy.
What Just Happened' closed the Cannes International Film festival last month and is based on Art Linson's memoirs. Robert De Niro stars as a frazzled producer and Catherine Keener, Stanley Tucci and John Turturro are among the key cast.
Linson and De Niro and Jane Rosenthal's Tribeca Productions produced alongside 2929 Productions.
'Although this movie is set in Hollywood, it's really a story about contemporary American life that all of us can relate to,' said Schwartz in a statement. 'I'm looking forward to working with 2929 and Magnolia to bring this smart, funny and authentic film to audiences across the country.'