According to producers, LaChanze (The Color Purple, Once On This Island, Ragtime) will portray Kate, "an elementary school teacher and new neighbor of Elizabeth, played by Menzel."
Additional casting will be announced.
David Stone, who also produced Wicked and Next to Normal, is shepherding the project about a woman on the cusp of 40, who moves to New York City to start fresh. It marks Menzel's first return to Broadway since her Tony-winning run in the 2003 musical Wicked.
The musical has music by Kitt, with book and lyrics by Yorkey. The writers earned the Tony Award and Pulitzer Prize for penning Next to Normal.
Here's how it's billed: "On the verge of turning 40, Elizabeth moves back to New York City, the ultimate city of possibility, intent on a fresh start – new home, new friends, and hopes for a resurgent career. But even in her carefully planned new life, the smallest decision or most random occurrence will impact her world in ways she never dreamt possible. Set against the ever-shifting landscape of modern day Manhattan, If/Then is a romantic and original new musical about how choice and chance collide and how we learn to love the fallout."