Ryan was born Rosalyn Bowen in Detroit, Michigan, the daughter of Gertrude and Thomas Bowen, who worked for the Board of Education. She is a 1969 graduate of Mackenzie High School. Ryan has starred in numerous Broadway musicals including: Ain't Misbehavin, Chicago, A Christmas Carol, Dreamgirls, One Mo' Time, and the 2006 revival of The Pajama Game. She is better known for her role as Amelia Hetebrink on Amen, Mrs. Dixon on Good News and Flo Anderson on All About the Andersons. She also guest starred on an episode on Barbershop. She was the voice of Thalia, the Muse of Comedy in Disney's animated film Hercules and Hercules: The Animated Series. She is the voice of Bubbie the whale in the 2008 animated television series The Marvelous Misadventures of Flapjack. She had roles in the films I Think I Love My Wife, The Invention of Lying and Waiting for Forever. She voices Kick's Teacher Ms. Fitzpatrick in the animated series Kick Buttowski: Suburban Daredevil. She was the voice of Witch Lezah in The Looney Tunes Show. She has also played Jake's female and feline counterpart Cake in the Adventure Time episodes; "Fionna and Cake", "Bad Little Boy", "The Prince Who Wanted Everything", and "Five Short Tables". She has also starred in TVOne's The Rickey Smiley Show.

She most recently starred on Broadway in Scandalous: The Life and Trials of Aimee Semple McPherson. In late May 2016 Ryan begun her 13th run in Chicago as Matron "Mama" Morton.