St. John was born Marco John Figueroa, Jr. in New Orleans, Louisiana, the son of Iris (née Davidson) and Marco Juan Figueroa, Sr. He has had many TV roles, starred in many TV-films and had roles on soap operas. He starred on Search for Tomorrow in 1975 as Joey Kimball, as Paul Stewart in 1969-70 on As the World Turns and in All My Children.