The 22-year-old moved to the capital from Wolfsburg on loan in August and has featured 18 times under Jos Luhukay this term, scoring once.
Cigerci, a Germany under-19 international, will join the club until 2017 having impressed during Hertha's return to the top flight.
"Hertha BSC has taken the option to purchase Tolga Cigerci and the 22-year-old is firmly committed until 2017," read a statement on Hertha's official website.
Despite being in the upper reaches of the Bundesliga for much of the campaign, Luhukay's men have faltered of late and slipped to 10th.
Hertha have not won any of their last eight league matches, although Cigerci was not too overly concerned by their most recent defeat - a 2-1 loss at Bayer Leverkusen on Sunday.
"I think we paid for the first 20 minutes (in which Hertha conceded twice). We showed good character after that and, with a bit of luck, we would have made it 2-2," he told the Bundesliga's official website.
