A member of the radical Hungarian reform party under Lajos Kossuth, Andrássy entered the Hungarian Diet in 1847. He commanded a battalion in the revolt against Austria of 1848–49. Fleeing into exile on Hungary's surrender, he was condemned in absentia to death and was hanged in effigy, but he obtained an amnesty in 1857 and returned. Andrássy thereafter supported Ferenc Deák in the negotiations leading to the dualist compromise of 1867. Appointed Hungarian prime minister and defense minister (Feb. 17, 1867), he was largely responsible for the final constitutional negotiations between Austria and Hungary.

Viewing the Slavs as a threat to his country, Andrássy became a staunch supporter of dualism and opposed Karl Siegmund von Hohenwart's (Hohenwart, Karl Siegmund, Graf von) scheme (1871) to raise the constitutional status of the lands of the Bohemian crown. He further cultivated relations with Germany as a counterweight to Russia and opposed the destruction of Turkey, which would have resulted in tremendous gains for the Slavic powers. On his insistence, Austria remained neutral during the Franco-German War of 1870–71.

When Emperor Francis Joseph abandoned his policy of revenge against Prussia, Andrássy became Austro-Hungarian foreign minister (Nov. 14, 1871). During his tenure Austria-Hungary's international position was strengthened considerably. He tried to avoid an increase in the monarchy's Slavic population, but, to prevent Russia from profiting alone from the Balkan crisis beginning in 1875, he agreed at the Congress of Berlin (1878) to Austria's occupation of Bosnia and Hercegovina. This act, highly unpopular in both Austria and Hungary, contributed to his decision to resign (Oct. 8, 1879). The previous day, however, he signed the fateful Austro-German alliance that was to link these two great powers until the end of World War I.

After his retirement, Andrássy remained in public life as a member of Hungary's upper house. His younger son and namesake also became a distinguished Austro-Hungarian political leader.