Manso de Velasco served as governor of Chile from November 1737 to June 1744, during which time he stood out for his numerous projects.

[clarification needed] Manso de Velasco was the viceroy of Peru during the reign of Ferdinand VI of the House of Bourbon, holding the office from 1745 to October 12, 1761.

On October 28, 1746 at around 10:30 at night, a major earthquake struck Lima and vicinity, resulting in one of the highest number of deaths for such an event in the area.

The aged and tired Manso de Velasco asked for permission to return to Spain for his retirement, and received a positive answer from the crown in 1761.

The British laid siege to the port, and Manso de Velasco, nominally the highest-ranking military officer in the area, found himself named the "Chief of the War Council" by the Governor of Cuba.

The sentences were not lenient, Manso de Velasco was condemned to 10 years of exile to 40 leagues from the Court, seizure of goods and he was made jointly responsible for compensating harmed Habaneros.