The delay has long been rumoured as producers take their time making sure the eighth and final season is appropriately epic and climactic.
Turner, who plays Sansa Stark in the hit fantasy show, merrily gave the sad news to Variety.
"I'm really excited. Game of Thrones comes out in 2019," she said.
Filming for Game of Thrones season eight has already begun, although it kicked off later than for previous seasons, and some of the final episodes will reportedly be feature film-length.
Casey Bloys, president of the show's broadcaster HBO, told Entertainment Weekly the delay will try and help ensure the final season is the biggest yet.
"When you see these battles in season seven, and what I imagine season eight will be, it's a big, big show," he said.
"One of the hallmarks of the show has been how cinematic it is. The show has proven that TV is every bit as impressive and in many cases more so, than film. What they're doing is monumental.
"I think this is the first show to prove that can be done - and we're the first people to pay for it."
HBO is also currently developing multiple Game of Thrones spin-off shows.