Parti populaire slovène
Korošec was vice-president in the first government of the Kingdom of Serbs, Croats and Slovenes in 1918. As the leader of the Slovenian People's Party he later collaborated in two right-leaning governments. Despite its defeat in 1920, the Slovenian People's Party was again victorious in Slovenia in 1924 and Korošec was chosen to be vice-president of the government. In 1924 and 1927, he was also minister for the interior. Korošec opposed the adoption of the Vidovdan Constitution and campaigned for greater autonomy for Slovenes within the Kingdom of Serbs, Croats and Slovenes until the Slovenian People's Party joined with Serbian radicals to form a centralist government and the idea was sidelined. Following Stjepan Radić’s assassination in 1928, in order to ensure more peace between ethnic groups the king called Korošec to lead the first government of Yugoslavia without a Serbian Prime Minister, but the monarch soon dismissed him when the :January 6th Dictatorship was proclaimed. Korošec was also a minister in Petar Živković’s government in 1929. He tried to resolve the crisis in the country by democratic means, but the government fell in 1930 under pressure from Slovenia.