Müller joined the Brazilian Army at age 19, eventually becoming an officer who participated in the Tenente revolts.

He was a close collaborator of Vargas since his rise to power in the Brazilian Revolution of 1930, which led to him being installed as the Chief of Police of the original Federal District in Rio de Janeiro.

[1] Before and during World War II, he was sympathetic to Nazi Germany, personally encouraging close cooperation between the Gestapo and Brazilian law enforcement.

He was dismissed from his post when Vargas switched sides, moving Brazil to the Allies against Adolf Hitler.

Together, they adopted de la Lastra's niece, Argentinian-born María Luísa Beatriz del.