Education and career
He studied law at the University of Granada and the University of Valladolid. He was rector of the Colegio Mayor del Arzobispo of Salamanca in 1766, 1768 and 1770. He taught Instituta at the University of Salamanca.
Already a doctor of law, between 1778 and 1780 he served as judge of the Real Audiencia of Chile. He was very active in this colony. He worked as an inspector of the works of the Santiago de Chile Cathedral, as Senior Judge over deceased property, as the protector of Convictorio Carolino and the Provincial Women's Hospital. He was known to own a small print shop for his private use, apparently the first or second operated in this country.
In 1781 de Rezabal y Ugarte was transferred to Lima to work as Mayor of crime. In this new destination he led the case against Túpac Amaru II, for the uprising that he had spearheaded. The decision in this case was published in 1783 by colonial order. de Rezabal y Ugarte also led other causes connected with this case, including another trial against Manuel Antonio Figueroa, called El Incognito.
While in Peru, de Rezabal y Ugarte occupied all kinds of positions, such as Director Royal of Studies at the University of San Marcos, Proprietary Judge and Dean Judge of the new Real Audiencia of Cuzco in 1786. This last position was not occupied at first as it was intended for the complicated trial prompted by the collapse which occurred at the mine in Huancavelica that year, killing 200 people. In that case the proceedings focused on embezzlement charges against the director of the institution, Francisco Marroquin.
He married in 1787 to Jane Catherine Micheo y Jiménez de Lobaton.
After taking on such notorious causes he aspired to fill a vacancy for judge of the Real Audiencia of Lima without much success, so he decided to hold the office of judge that was awaiting him in Cuzco in 1791.