Hartmann was born 1977 in Oberhausen and, on a scholarship of the Friedrich Ebert Foundation, studied jurisprudence without achieving an academic degree.

[1] Since the 2021 elections, Hartmann has been serving as his parliamentary group's spokesperson for internal affairs.

[3] That same year, he joined the Commission for the Reform of the Electoral Law and the Modernization of Parliamentary Work, co-chaired by Johannes Fechner and Nina Warken.

[4] In addition to his committee assignments, Hartmann has been a member of the German delegation to the Franco-German Parliamentary Assembly since 2019.

[5] From 2018 to 2021, Hartmann served as chairman of the SPD in North Rhine-Westphalia, Germany's most populous state.