The longest tournament chess game, in terms of moves, ever to be played was Ivan Nikolic vs. Goran Arsovic in Belgrade, Serbia in 1989. The game lasted for 269 moves and took 20 hours and 15 minutes to complete. It ended in a draw.

The longest decisive tournament game was Viktor Kortchnoi vs. Laurent Fressinet, Villandry, France in 2007, which Kosteniuk won in 237 moves and lasted a little more than two hours. Fressinet could have claimed a draw under the fifty-move rule, but did not do so since neither player was keeping score, it being a rapid chess game.

source