Aleksić began his political career as a member of the United Regions of Serbia, serving as president of its Trstenik board in the early 2010s. The UnitedRegions of Serbia won the greatest number of seats in Trstenik's 2012 municipal elections and formed a coalition government with the Serbian Progressive Party, New Serbia, the Socialist Party of Serbia, and the Party of United Pensioners of Serbia. Aleksić was selected as head of the municipality and served in this role for the next four years. He issued a declaration that genetically modified food would not be produced in the municipality and opposed nickel mining on the grounds that it would jeopardize several local villages. His term ended following the 2016 municipal elections, when the Progressive Party, the Socialist Party, and the Serbian Renewal Movement formed a new coalition. He continues to serve in the Trstenik municipal assembly. Aleksić was a URS spokesperson at the national level during this time and received the eleventh position on its electoral list in the 2014 Serbian parliamentary election. The list did not cross the threshold to win representation in the assembly. Aleksić left the party later in the year and served on the steering committee of a breakaway group originally called the People's Party of Serbia. In February 2015, this group formally constituted itself as the People's Movement of Serbia with Aleksić as leader. He received the eighth position on the Alliance for a Better Serbia list in the 2016 parliamentary election and was elected when it won thirteen mandates. The list was principally an alliance of the Liberal Democratic Party, the Social Democratic Party, and the League of Social Democrats of Vojvodina; Aleksić was the only People's Movement candidate elected. The Serbian Progressive Party and its allies won the election, and Aleksić serves in opposition. In October 2017, he permitted the People's Movement of Serbia to be re-registered as the People's Party under Jeremić's leadership, allowing the new party to bypass the usual registration process. Aleksić was selected as vice-president of the People's Party at its founding convention the same month. For most of the 2016–20 parliament, Aleksić was the deputy leader of the Social Democratic Party–People's Party parliamentary group, which had five members. This group dissolved in 2020. He is a member of the parliamentary committee on agriculture, forestry, and water management; a deputy member of the committees on Kosovo-Metohija and the rights of the child; and a member of the parliamentary friendship groups with Austria, Belarus, China, Croatia, Germany, Italy, Poland, Romania, Russia, Slovenia, Switzerland, and the United States of America. Along with other opposition parties, the People's Party has boycotted the National Assembly since 2019 and is boycotting the 2020 Serbian parliamentary election, accusing the governing Progressive Party of undermining Serbia's democratic institutions conditions and charging that conditions do not exist for free elections. Aleksić has been prominent among opposition figures in calling for a total electoral boycott at all levels of government.
