He was born in Sieverodonetsk in Ukraine to Roman and Tanja Molleker and moved to Oranienburg in Germany when he was three years old.

[3] Molleker made his ATP main draw debut at the German Open in Hamburg after defeating Casper Ruud and Leonardo Mayer, who later won the tournament as a lucky loser, in the qualifying rounds.

Molleker won his first ATP Challenger Tour title as a wildcard at the Heilbronner Neckarcup, defeating Jiří Veselý in the final.

[6] Molleker made his Grand Slam debut at the 2019 Australian Open, battling through three qualifying rounds before falling to world No.

179, he also received a wildcard for the main draw at the 2024 BMW Open and defeated qualifier Francesco Passaro for his fifth ATP win.