He was admitted into the Mexico City Cathedral choir in 1625, where he studied early European Gregorian chant and organum under organist and choirmaster Antonio Rodriguez Mata.
This move also granted Capillas an opportunity to further study the music of European medieval and early renaissance masters including Tomás Luis de Victoria, Clément Janequin, and Giovanni Palestrina.
In 1648, Capillas was brought back to Mexico City to assist Fabián Pérez Ximeno, who had succeeded Mata as the organist and choirmaster of the Catedral de México.
In this role, Capillas assisted Pérez Ximeno, oversaw the installation of a new grand organ (built in the style of the ones at Puebla) and developed of a children's choir at the Cathedral.
Four days later, López was appointed choirmaster and principal organist "in recognition of his great sufficiency and ability for the ministries" at the Catedral de México.