The broadcaster revealed the news as the second season of the tale of adolescent highs and lows came to a close on Tuesday night.
Writer Lisa McGee, who used her own childhood as the basis for the show, said she was thrilled her band of "eejits" would continue their on-screen adventures.
The show follows the antics of a group of friends growing up in Londonderry around the time of the IRA and loyalist ceasefires.
In Northern Ireland the series two launch became the most-watched programme across all channels since the first series aired.
Channel 4's director of programmes Ian Katz said: "At a time of great uncertainty about the future of the country thank God we have one unequivocally good piece of news to look forward to: the Derry Girls will be back to make our lives a bit brighter and more fun."
Head of comedy at the channel Fiona McDermott said: "It's no surprise that Derry Girls continues to delight a growing legion of fans - a combination of magical writing and adorable characters make this show both timely and timeless.
"We're delighted to confirm a third series - don't tell Ma Mary, but I'm breaking open the Christmas cupboard in celebration."