In his diary for 1927, American diplomat Robert Heingartner who served in Lithuania recorded that "Colonel Daukantas is said to be so powerful in the army that no government could last a day without his support.
He was Lithuanian Consul General in Rio de Janeiro (1932–1935) and Minister Plenipotentiary of South America (1936–1939).
On October 20, 1932, Daukantas co-signed a Treaty # 3542 with Carlos Saavedra Lamas under the League of European Nations which insured a convention or treaty between the Argentine Republic and the Independent Republic of Lithuania concerning reciprocity with respect to the payment of compensation for industrial accidents signed at Buenos Aires on October 20, 1932.
Daukantas was a Member of the States Council, Chargé d'Affaires for Argentina, Brazil, Paraguay, and Uruguay, (1930 -1935).
In 1941 Daukantas was arrested, imprisoned, and tortured during the Soviet rule of Lithuania, and persecuted by the Nazi German Gestapo in 1942-1944 during their occupation.