[4] Aleksić began his political career as a member of the United Regions of Serbia, serving as president of its Trstenik municipal board in the early 2010s.

[7] He issued a declaration in 2013 that genetically modified food would not be produced in the municipality, and he opposed nickel mining in the area on the grounds that it would jeopardise several local villages.

[12][13][14] The group formally constituted itself as the People's Movement of Serbia in January 2015, and Aleksić was chosen as its leader in February.

The Progressives afterward formed a new administration with the Socialists and the Serbian Renewal Movement (SPO), and Aleksić's term as mayor came to an end.

Aleksić, as the NPS's leader, was given the eighth position and was elected when the list won thirteen seats; he was the only member of his party to receive a mandate.

[22] The Progressive Party and its allies won the election, and Aleksić served in opposition as deputy leader of a SDS–NPS parliamentary group that had five members in total.

[25] During the 2016–20 parliament, various opposition parties accused Serbian president Aleksandar Vučić and Serbia's SNS-led administration of undermining the country's democratic institutions.

Aleksić was one of the most prominent opposition figures calling for a total election boycott in all jurisdictions and at all levels of government, rather than participating in what he considered a sham democracy.

[29] The SNS and its allies won the election, and Aleksić initially led the People's Party assembly group in opposition.

[34] Both Aleksić and Tepić focused on anti-corruption issues during the campaign; on one occasion, Aleksić was quoted as saying, "We have to [...] introduce a functioning system of institutions, so that those who are responsible for looting the state, who generated crime and violence, who destroyed public companies and institutions, who brought ministers to learn the job, all these people will have to answer.

[41] In November 2022, Aleksić called on the European Union to be "just as vocal on issues important to the lives of Serbian citizens, such as the fight against crime and corruption and freedom of the media, as it is when it points to the need to harmonize Serbia's foreign and security policy with the EU".