When Martin was 12, his mother apprenticed him to a barber-surgeon. He learned how to cut hair and also how to give basic medical care, which was usual for barbers at that time. After a few years in this medical apostolate, St. Martin applied to the Dominicans to be a "lay helper," not feeling himself worthy to be a religious brother. After nine years, the example of his prayer and penance, charity and humility led the community to request him to make full religious profession. Many of his nights were spent in prayer and penitential practices; his days were filled with nursing the sick and caring for the poor. He treated all people regardless of their color, race or status. He was instrumental in founding an orphanage, took care of slaves brought from Africa and managed the daily alms of the priory with practicality as well as generosity. He became the procurator for both priory and city, whether it was a matter of "blankets, shirts, candles, candy, miracles or prayers!" When his priory was in debt, he said, "I am only a poor mulatto. Sell me. I am the property of the order. Sell me."
Side by side with his daily work in the kitchen, laundry and infirmary, Martin's life reflected God's extraordinary gifts: ecstasies that lifted him into the air, light filling the room where he prayed, bilocation, miraculous knowledge, instantaneous cures and a remarkable rapport with animals. His charity extended to beasts of the field and even to the vermin of the kitchen. He would excuse the raids of mice and rats on the grounds that they were underfed; he kept stray cats and dogs at his sister's house.
Many of his fellow religious took him as their spiritual director, but he continued to call himself a "poor slave." He was a good friend of another Dominican saint of Peru, Rose of Lima.
O God, whose blessed Son became poor that we through his poverty might be rich: Deliver us, we pray thee, from an inordinate love of this world, that, inspired by the devotion of thy servant St. Martin de Porres, we may serve thee with singleness of heart, and attain to the riches of the age to come; through the same thy Son Jesus Christ our Lord, who liveth and reigneth with thee, in the unity of the Holy Spirit, one God, now and for ever. Amen.