The movie is set in the late 1960s as Garland arrives in London for a run of sell-out concerts.
As well as Zellweger in the lead role, the cast includes Jessie Buckley ("War and Peace"), Finn Wittrock ("American Horror Story") and Michael Gambon ("Harry Potter").
Garland's dates at the Talk of the Town nightclub came toward the end of the icon's long career and shortly before her death. The movie will recount her performances, with some of her best-known numbers, including "Somewhere Over the Rainbow."
The film also delves into Garland's behind-the-scenes battles with management, her relationships with musicians and fans, and the unfolding family drama that provided the backdrop to the London performances. She died in London in June 1969.
"Judy" is a Pathe, BBC Films and Ingenious Media presentation of a Calamity Films Production. Principal photography is now underway and is being shot in London.
British stage director and Tony nominee Rupert Goold is directing "Judy" from a script by Tom Edge ("The Crown").