After the death of his father, he became a gentleman of the Board of Manuel I and João III, captain-general of Cartaxo, young nobleman and knight of the royal house.

[3] This last source claimed that this event was decisive in leading to the utilisation of the island as a regular stopover for rest and replenishment for ships en route from India to Europe.

However, this seems doubtful because when Estêvão da Gama arrived at St Helena expedition in 1503 his clerk Thomé Lopes)[4][5][6] identified St Helena's geographic position with reasonable accuracy when he quoted its distance and direction with respect to locations such as Ascension, Cape Verde, São Tomé and the Cape of Good Hope.

The island's location with respect to Ascension and the Cape of Good Hope was likewise known following the 1505 Portuguese expedition led by Francisco de Almeida.

Dom Garcia died before the end of his mandate as viceroy on April 3, 1540, in Cochin and is buried in the chancel of the Cathedral of Goa.