 Chagas was the son of José Justiniano das Chagas, a coffee farmer from Minas Gerais, and Mariana Cândida Chagas, both of Portuguese descent.After his secondary studies at Itu, São Paulo and São João del Rei, he enrolled in the School of Mining Engineering at Ouro Preto, but changed to the Medical School of Rio de Janeiro in 1897, influenced by his uncle, who was a physician and owner of a hospital in that city.He graduated in 1902 and got his M.D.