Co-created and executive-produced by Amy Poehler, Josh Bycel and Jonathan Fener, the series stars Natasha Lyonne.
David Wain directs the single-camera comedy.
"Old Soul," according to Deadline, centers on a "reformed wild child Nadia (Lyonne) who has a business caring for the elderly and feels she has more in common with her colorful old clients than she does with people her age." Moreno will play a client named Rita, who is described as "a sexy old gal and ... flamboyant, larger-than-life Broadway vet who has been happily married to her writing partner/husband for over 50 years."
The singing actress was most recently seen on stage in the critically acclaimed, extended engagement of Rita Moreno: Life Without Makeup, a music-kissed biographical show, at Berkeley Repertory Theatre.