He assisted his brother in the conquest of the Incas and defended Cuzco against the attacks of Manco Capac (1536–37). In 1538 he was appointed governor of Quito. The first viceroy of Peru, Blasco Núñez Vela, proclaimed the New Laws in 1542, drafted by Las Casas, to protect Indian rights. Gonzalo became leader of conquistadores opposed to the New Laws and in the ensuing civil war defeated and executed the viceroy in 1546. He was offered a royal pardon by the new viceroy, but rejected it, and was beheaded in 1548 after his army had deserted him.