Born 16 August 1990 Dolný Kubín, Šeliga studied law at the University of Trnava, where he obtained a PhD degree.

[4] In 2017, he founded the civic initiative Remember (Slovak: Pamätaj) to oppose the weakening of the National Memory Institute and promote the study of crimes of totalitarian regime.

[3][5] Following the murder of Ján Kuciak, Šeliga was one of the main organizers of massive anti-government protests where he refused any political ambitions in the future.

[6][7] In June 2019, Šeliga was one of the co-founders of For the People led by the president Andrej Kiska,[8] serving as deputy chairman until March 2023.

[10] In May 2021, Šeliga resigned as Deputy Speakership after pictures of him, his fellow MP Jana Žitňanská, and the governor of the Bratislava region Juraj Droba spending time together in a restaurant that should have been deleted due to the COVID-19 pandemic were published by the tabloid press.