He was born in San Sebastián, where he began studying violin and viola. He continued his studies at the Reina Sofía School of Music in Madrid, the University of Toronto, the Hans Eisler Hochschule für Musik in Berlin, and the Amsterdam Conservatory.

He has won several prizes in competitions, including the Pablo Sarasate National Prize, the Isidro Gyenes National Violin Competition, the Julio Cardona International Competition in Portugal, the Vittorio Gui Competition in Florence, and the Bonporti Prize for Baroque violin in Rovereto, Italy.

Mercero has conducted, as concertmaster, the City of Granada Orchestra, the Burgos Symphony Orchestra, the Salamanca Baroque Orchestra, and the Seville Baroque Orchestra.

He has been guest concertmaster of the Oviedo Opera, the Academia Bizantina, I Barocchisti, the Gran Canaria Philharmonic Orchestra, the Vallés Symphony Orchestra, the Royal Chapel of Madrid, the Cetra Barockorchester Basel, and the Kammerorchester Zurich. He also collaborates regularly with groups such as Café Zimmermann, Le Concert des Nations, Le Parlement de Musique, Il Complesso Barocco, and The Rare Fruits Council. He is currently the director of the group Musica Boscareccia, with which he recently recorded a CD dedicated to the work of Francesco Corselli. He also teaches at JONDE (National Association of Spanish Music) and at the Academy of Early Music at the University of Salamanca. He currently teaches string quartet at Musikene.