The seven-week shoot will be held in and around London for five weeks with two weeks at Ealing Studios.
Bharat Nalluri, whose most recent credit is the miniseries Tsunami: The Aftermath, is directing.
David Magee and Simon Beaufoy adapted the script from the novel by Winifred Watson. The 1939-set story follows a middle-aged governess in London who suddenly finds herself mingling with high society.
The cast also features Amy Adams, Ciaran Hinds, Shirley Henderson, Lee Pace, Mark Strong and newcomer Tom Payne.
Nellie Bellflower and Stephen Garrett are producing. McDormand, Frank Frattaroli and Paul Webster are executive producing, while Focus senior vice president, production John Lyons will oversee for the company.
Focus will hold worldwide rights on the film, which is a Kudos Pictures/Keylight Entertainment Production.
Focus CEO James Schamus said: 'Miss Pettigrew Lives for a Day is a perfect love story for Focus - sophisticated and heartfelt at the same time, and a tremendous showcase for Fran McDormand, Amy Adams, and their spectacular castmates.'