Ralph was born in Waterbury Connecticut to an African American father and a Jamaican mother. In 1973, she was crowned Miss Black Teen-age New York. At 19, Ralph was the youngest woman to ever graduate from Rutgers University. Also that year she was named as one of the top 10 college women in America by Glamour magazine. Initially she hoped to study medicine, but after dealing with cadavers in a premed class and winning a scholarship in a competition at the American College Theater Festival, she quit medicine for the performing arts. Many years later, she served as the commencement speaker at Rutgers for the Class of 2003.
Ralph began her career on the stage and was nominated in 1982 for a Tony Award for Best Actress in a Musical for her role as "Deena Jones" in Dreamgirls. In 1984, Ralph released her only album In the Evening, with it's title track peaking at #6 on the Billboard charts.
Rapl starrred in Oliver & Company (vocals for "Rita"), The Mighty Quinn, Mistress (1992), The Flintstones, Deterrence and Unconditional Love.
On television, she is known for playing "Etienne Toussaint-Bouvier" on Designing Women, and later "Dee Mitchell" on Moesha. Ralph produced Divas Simply Singing, which has become an important AIDS fundraiser.
In July 2004, Ralph was inducted as an honorary member of Delta Sigma Theta sorority at the 47th National Convention in Las Vegas, Nevada.