In 1940, when she was thirteen years old, she won the contest in a local radio station, Los aficionados de WPAB, an amateur show for performers.
That same year she began her night club appearances, initially at the Vodoo Room of the Normandy Hotel as lead singer of the Joe Vallejo Combo.
As a singer, she sang in variety shows, such as Fiesta a las 9, Fandango Rheingold and Caravana, aired through the two tv stations at the time, WKAQ and WAPA.
In 1956, she played Angustias in the successful Cuando los hijos condenan, a milestone soap opera that led to a complete change in the length of the genre.
After supporting roles in soap operas, such as Sangre en la calle, Divorcio and Yo maté a una santa, Romero got top billing in Rafael Heredia: Gitano, opposite Esther Sandoval and Argentinian actor Enzo Bellomo.
On 19 May 1960, Romero made her official onstage debut with the play En el Principio la noche era serena (At the Beginning the Night was Serene), written by Gerard Paul Marín, and performed at San Juan's Municipal Teatro Tapia.
In 1963, she recorded her first album as a singer, Marta Romero Canta (SALP-1336), This LP includes, the boleros "Es tarde ya" (It's Too Late Now), composed by Sylvia Rexach and "¿Qué sabes tú?"
Romero retired as an actress and bolero singer because she embraced the Christian faith in the Puerta del Cielo (Heaven's Door) church, located in Caguas, Puerto Rico in 1975.