Kosor started working as a journalist, following her graduation from the Zagreb Faculty of Law. During the Croatian War of Independence, she hosted a radio show dealing with refugee problems and disabled war veterans. She joined the centre-right Croatian Democratic Union (HDZ) in 1989 and quickly climbed up the party hierarchy. In 1995 she was elected party vice-president and was elected to serve in Parliament for the first time. After the death of president and longtime HDZ leader Franjo Tuđman, Kosor supported Ivo Sanader's successful party leadership bid in 2000. Three years later, her party won the parliamentary election and Kosor became the Minister of Family, Veterans' Affairs and Inter-generational Solidarity in the Sanader first and, later, Sanader second cabinet, during which time she served as deputy prime minister as well. In the 2005 presidential election she ran as a representative of the HDZ, but lost to incumbent President Stjepan Mesić in the second round. After the abrupt resignation of Sanader, Kosor managed to form a functioning parliamentary majority and was approved to her new post as prime minister in July 2009, also becoming leader of her party. Kosor was the party's candidate for prime minister in the 2011 general election, but HDZ lost in a landslide over the centre-left Kukuriku coalition, led by the Social Democratic Party. Kosor handed power to the new Prime Minister, Zoran Milanović, in December 2011.