Serna was born as Asunción Rodes Serna in Barcelona, Spain. She married her co-star in Sharpe's Company, Scott Cleverdon, who portrayed Lieutenant Harry Price in the film. She has also appeared in the 2003 ITV television drama on King Henry VIII as Catherine of Aragon, and the Spanish TV series Aquí no hay quien viva.
She has written two books on acting technique, "Screenacting" and "Monologues in V.O." and currently teaches courses "Acting for Camera", "Directing Actors" and "The Script and the Actor" at various acting schools and workshops. She has also served as president of AISGE, Actores e Intérpretes - Sociedad de Gestión de España, Spain's principal actors' union.