Baumbach was nominated for an Oscar for his original screenplay for "The Squid and the Whale," which he also directed. Stiller was most recently seen in the big-screen comedy "Tropic Thunder."
Focus chief executive officer James Schamus announced that production on the film began last week.
"It's a privilege and a pleasure to finally be making a movie with Scott, Jennifer and Noah, and one that will showcase Ben as an actor," Schamus said in a statement. "This script has the hallmarks of Noah's best work, and then some; heart and soul interlaced with biting wit. Filmgoers worldwide will find themselves emotionally engaged by and with these splendidly realized characters."
"At a crossroads in his life, Roger Greenberg (Stiller) ends up housesitting at his brother's home in Los Angeles," the studio said of the film in a release. "There, he strikes up an unlikely friendship with his brother's assistant Florence (Greta Gerwig,) an aspiring singer. Florence and Greenberg's encounters lead to an uncertain and wonderfully vulnerable courtship."
The film is to co-star Leigh, Rhys Ifans, Mark Duplass, Brie Larson and Juno Temple.