Miloševic's mentor and close personal friend Ivan Stambolic was the party leader in the Serbian section of the ruling League of Communists of Yugoslavia. In September 1987, Stambolic became the President of Serbia and supported Miloševic in the elections for the new leader, to the dismay of the other leaders in the party. Stambolic spent three days advocating Miloševic's election and finally managed to secure him a tight victory, the tightest ever in the history of Serbian Communist Party internal elections.
Contrary to the liberal reforms of Communism in the Soviet Union at the time, Miloševic quickly took a hard line against liberalism in the party and proceeded to use such a policy to eliminate his political adversaries.
Dragiša Pavlovic, Miloševic's fairly liberal successor at the head of the Belgrade Committee of the party, opposed his policy towards the solving of the issues of the Kosovo Serbs, calling it "hastily promised speed". Miloševic denounced Pavlovic as being soft on Albanian radicals, contrary to advice from Stambolic. In 23 September/24th, on the subsequent eighth session of the Central Committee, one that lasted around 30 hours, and was broadcast live on the state television, Miloševic had Pavlovic deposed, to the utter embarrassment of Ivan Stambolic, who resigned under pressure from Miloševic's supporters a few days later.
In February 1988, Stambolic was officially voted off the position and Miloševic could take his place. Miloševic would later be charged with ordering the murder of Stambolic. Ivan Stambolic was kidnapped in the summer of 2000; his body was found three years later. As of 2004, members of Serbian criminal gangs close to Miloševic are indicted at the Belgrade court for this murder (among others).
On the 14th Congress of the League of Communists of Yugoslavia in January 1990, the delegation of Serbia led by Miloševic insisted on the reversal of 1974 Constitution policy that empowered the republics and rather wanted to introduce a policy of "one person, one vote", which would empower the majority population, the Serbs. This caused the Slovenian and Croatian delegations (led by Milan Kucan and Ivica Racan, resp.) to leave the Congress in protest and marked a culmination in the rift of the Yugoslav ruling party.
Miloševic presided over the transformation of the League of Communists of Serbia into the Socialist Party of Serbia (July 1990) and the adoption of a new Serbian constitution (September 1990) providing for the direct election of a president with increased powers. Miloševic was subsequently re-elected president of the Serbian Republic in the direct elections of December 1990 and December 1992.
In the first free parliamentary elections of December 1990, Miloševic's Socialist Party won 80.5% of the vote. The ethnic Albanians in Kosovo largely boycotted the election, effectively eliminating even what little opposition Miloševic had. Miloševic himself won the presidential election with even higher percentage of the vote.