Trumbić was born in Split in the Austriancrownland of Dalmatia and studied law at Zagreb, Vienna and Graz. He practiced as a lawyer, and then, from 1905 as the city mayor of Split. Trumbić was in favor of moderate reforms in Austro-Hungarian Slavic provinces, which included the unification of Dalmatia with Croatia-Slavonia. After the assassination in Sarajevo of Archduke Franz Ferdinand and the invasion of Serbia by Austria-Hungary, Trumbić became the prominent Yugoslav nationalist leader during World War I, and led the Yugoslav Committee that lobbied the Allies to support the creation of an independent Yugoslavia. Trumbić negotiated with Serbian Prime MinisterNikola Pašić to have the Kingdom of Serbia support the creation of a Yugoslav state, which was delivered at the Corfu Declaration on 20 July 1917 that advocated the creation of a united state of Serbs, Croats and Slovenes that would be led by the Serbian House of Karađorđević. In 1918 he became foreign minister in the first government of the Kingdom of Serbs, Croats and Slovenes. At the Versailles conference after World War I, Trumbić had to represent Yugoslav concerns in the face of Italian territorial ambitions in Dalmatia. In spite of his support for a united Yugoslavia, Trumbić opposed the 1921 constitution over his belief that it was too centralized and allowed Serb hegemony over Yugoslavia. Trumbić was one of 35 representatives to vote against the constitution amid a wide boycott of the National Assembly by opposition parties. Trumbić grew steadily disillusioned with the Yugoslav government over time which he saw as Serb-dominated. He was elected for the last time in the 1927 elections on the list of the Croatian Bloc representing Zagreb together with Ante Pavelić. In 1929, claiming to bring an end to the ongoing bickering between the Serbian and the Croatian representatives within the kingdom, King Alexander of Yugoslavia staged a coup d'état and banned all political parties, and removed the individual nationalities Serb and Croat from the bigger picture. He renamed the land Yugoslavia, and abrogated the constitution to establish a royal dictatorship. Trumbić was by now in retirement in Zagreb. King Alexander's division of Croatia-Slavonia and Dalmatia into oblasts and then into banovinas, countered all previous reforms Trumbić had sought. In a September 1932 interview with The Manchester Guardian Trumbić wondered whether Croatia should separate from the Kingdom of Yugoslavia and pursue a union with Austria. In November 1932 Trumbić edited the Zagreb Points, a series of demands put forth by the Peasant-Democratic coalition to counter Serbian hegemony. With the arrest of Croatian Peasant Party leader Vladko Maček in April 1933 Trumbić and Josip Predavec became the caretaker heads of the party. With Predavec's assassination on 14 July, Trumbić was essentially the head of the party in Maček's absence. According to Henri Pozzi, Trumbić later regretted the end of Austria-Hungary, as the South Slav state he had helped to create proved incapable of his intended reforms.
