After the Sultan’s decree acknowledging the title of Prince Mihailo Obrenović at the end of 1839, the family returned to Serbia. Alexander joined the Headquarters of the Serbian Army, and was promoted to the rank of Lieutenant and appointed as adjutant to Prince Mihailo.
After the political conflicts caused by disrespect of the so-called "Turkish constitution," and Miloš Obrenović's and then Mihailo Obrenović's abdications, Aleksandar Karađorđević was elected the Prince of Serbia at the National Assembly in Vračar, a municipality in modern Belgrade, on 14 September 1842. Having had his title acknowledged by Russia and Turkey, Prince Aleksandar started the reforms and founded a number of new institutions in order to improve the progress of the Serbian state. He implemented the code of civil rights, introduced the regular Army, built a cannon foundry, improved the existing schools and founded new ones, as well as established the National Library and National Museum. It was Councillor Lazar Arsenijević Batalaka who, in 1845 introduced Ilija Garašanin to Prince Aleksandar. During the Hungarian Revolution in Vojvodina, in 1848, Prince Aleksandar Karađorđević sent Serbian volunteers under the command of Stevan Knićanin to help the Serbs’ struggle for autonomy. As a follow-up of the national-political movements of 1848, the pan-slavistic idea of a Yugoslav Monarchy emerged. The "Načertanije" document, written as a Serbian political program by Ilija Garašanin four years earlier, made the mission of replacing the Austrian and Turkish domination of all Southern Slavs with the Serbian rule under the banner of "Serbia." Throughout his reign, Prince Alexander was troubled with Obrenović plots. By his refusal to take part in the Crimean War as an ally of the French, British and Ottoman Empires against the Russian Empire. The result was his overthrow and departure into exile in 1858 by the winners of the Powers in the war and bringing the rival Obrenović dynasty to the throne of the Principality of Serbia. He was awarded Ottoman Order of Glory and Order of Distinction.
Abdication
In internal policy Prince Aleksandar came into conflict with the members of the Council, which culminated in the convocation of the Saint Andrew's Day Assembly, in December 1858, which forced him to abdicate. Prince Alexander died in Timișoara on 3 May 1885. He was buried in Vienna, and his earthly remains were moved in 1912 to the Memorial Church of St. George built by his son Petar I Karađorđević, in Oplenac, Serbia.
