[1] He entered the Brazilian foreign diplomatic service; his first commission was the secretary of the Immigration Service, and the contact at that time, the Baron of Rio Branco made him Secretary of the Rio Branco mission which established the boundaries of Brazil and Argentina and the boundary with French Guiana and the British Guyana.

[1] He was Secretary of Legation at the Holy See in 1900 and minister in Lima in 1906, where he instrumental in preparing for the policy of Rio Branco crowned by the Treaty of Petropolis.

In 1910, he was Ambassador on special mission representing Brazil in Argentina's independence centenary and the centennial celebrations of Chile.

Resolved by the Senate and House of Representatives of the United States of America in Congress assembled, That the thanks of Congress to their excellencies be, and they are hereby, presented to their excellencies Señor Domício da Gama, Señor Rómulo S. Naón, and Señor Eduardo Suárez for their generous services as mediators in the controversy between the Government of the United States of America and the leaders of the warring parties in the Republic of Mexico.

That the President of the United States is hereby authorized and requested to cause to be made and presented to their excellencies Señor Domicio da Gama, Señor Rómulo S. Naón, and Señor Eduardo Suárez suitable gold medals, appropriately inscribed, which shall express the high estimation in which Congress holds the services of these distinguished statesmen, and the Republics which they represent, in the promotion of peace and order in the American continent.On November 27, 1912, De Gama was married to American heiress Elizabeth (née Bates) Volck Hearn at 856 Fifth Avenue in New York City (the home of U.S. Steel President Elbert Henry Gary)[4] by Mayor William Jay Gaynor.