Sergej was born in Mostar, SR Bosnia and Herzegovina, SFR Yugoslavia, in the family of actor Tomislav Trifunović and lawyer Slobodanka.
His younger brother is actor Branislav Trifunović.
Sergej’s father in his career has often moved, so Sergej lived in Mostar, Užice, Kruševac and Belgrade.
In 1990 Trifunović enrolled in Belgrade Faculty of Drama Arts in class of professor Vladimir Jevtović. His fellow students were Nataša Ninković, Vojin Ćetković and Nebojša Glogovac.