 Hernandarias was born in Asunción, colonial Paraguay as the second son of María de Sanabria and Martín Suárez, an officer under Álvar Núñez Cabeza de Vaca.He had a sister, Juana de Saavedra, who later married Juan de Garay, the father of Jerónima de Contreras.His maternal grandparents were Diego de Sanabria and Mencia Calderón de Sanabria, who were wealthy from their holdings in Paraguay.