By the end of the war, Krstelj became a member of the National Council of Slovenes, Croats and Serbs—the body established with the aim of political unification of the South Slavs.
In the organisation, Krstelj advocated speedy unification of South Slavic lands formerly part of Austria-Hungary (including Croatia-Slavonia and Dalmatia) with the Kingdom of Serbia to prevent occupation of the eastern coast of the Adriatic Sea, i.e. Dalmatian coast, by the forces of the Kingdom of Italy enforcing provisions of the Treaty of London.
[1] Following the end of World War I and the dissolution of Austria-Hungary, the National Council of Slovenes, Croats and Serbs appointed Krstelj a member of the three-member provincial government of the former Austro-Hungarian crown land of Dalmatia, along with Josip Smodlaka and Vjekoslav Škarica (with deputies Prvislav Grisogono, Uroš Desnica, and Jerko Machiedo).
The provincial government administered the region in the run-up to the arrival of Allies of World War I and their occupation of the eastern Adriatic in 1918.
Krstelj held leading offices in the Democratic Party until 1927 and he was a government minister of religion in 1921–1922.