The US star, 49, will play female benefactor Anne who serves up a “lucrative, but dubious offer to a cash-strapped pair of San Francisco newlyweds” in the 10-part series.
Zellweger can be seen in a white dress and heels in first look images ahead of the show which drops next month.
What/If explores the ripple effects of what happens when acceptable people start doing unacceptable things, according to the synopsis.
The trailer introduces fans to the newlyweds, who are thought to be played by Jane Levy and Blake Jenner, and sees Zellweger’s character ask: “What if I made you an offer too extraordinary to refuse? For anything, and anyone, to be yours for the taking. The players are all arranged. What would you risk for a chance to have it all?”
Samantha Ware, Keith Powers, Daniella Pineda, Juan Castano, John Clarence Stewart and Dave Annable also star in the Phillip Noyce directed series which was penned by Revenge creator Mike Kelley.
WHAT/IF marks Zellweger’s first TV acting gig, bar a voice role on King of the Hill in 2001.
WHAT/IF will launch exclusively on Netflix on May 24