"It's become clear to us that this game is much more ambitious than we originally envisioned," the Naughty Dog developers wrote.
"So we've made the difficult choice of pushing the game's release date," they said. "Giving us a few extra months will make certain that Uncharted 4: A Thief's End not only meets the team's high standards, but the high standards that gamers have come to expect from a Naughty Dog title."
The pair added that "we know the extra wait will be excruciating," but believes the extra time will be worth it. "The team at Naughty Dog will be heads down working through 2015 making sure that Nathan Drake's story gets the closure it deserves."
Announced in November 2013, Sony said at E3 2014 that the fourth game in its exclusive Uncharted series would release sometime this year. The last entry in the series was 2011's Uncharted 3: Drake's Deception on PlayStation 3.
For more on Uncharted 4: A Thief's End, see this gameplay video from PlayStation Experience in December.