The 20th Century Fox TV and NBC comedy, co-written by "Glee"'s Ryan Murphy and Allison Adler, will also be directed by Murphy.
The single-camera project is described as "a heartwarming comedy about a blended family of a gay couple and the woman who becomes a surrogate to help them start a family."
Rannells' previous Broadway outings include leading roles in Jersey Boys and Hairspray. He received a Tony nomination for his performance in Mormon.