Albion climbed back into the Championship play-off places after the win, which left the visitors languishing in the bottom three.
It was the only highlight of a dreadful encounter.
It looked like both sides would cancel each other out, and the stalemate would have been no surprise when you consider the form of the clubs heading into the game.
Albion had failed to score in five of their last league fixtures, while Forest had drawn a blank in four of their last six.
But Buckley broke the trend in the second minute of injury time after being teed up by Craig Mackail-Smith.
Mauricio Taricco went straight back into the Brighton starting line-up on his return from a ban. The player/assistant manager replaced Inigo Calderon, who served his own suspension.
The 38-year-old's recall was one of four changes made by boss Gus Poyet as fellow defender Gonzalo Jara, midfielder Craig Noone and striker Billy Paynter also came back into the team. Romain Vincelot, Ryan Harley and Will Hoskins were the other players to make way.
Forest also made four changes. Garath McCleary replaced Lewis McGugan to make his first appearance of the season after recovering from injury, while Jonathan Greening was also restored to the midfield for the suspended Andy Reid.
Injury ruled Joel Lynch out against his former club so Chris Gunter filled in at full-back and Radoslaw Majewski got the nod ahead of Robbie Findley.
Little happened in the first half. Paul Anderson had a speculative shot from way out after 14 minutes and Majewski sent a 25-yard free-kick over the crossbar three minutes before the break.
The second half was not much better. Marcus Tudgay and McCleary both had chances within five minutes of the restart. Both missed the target when they should have done better.
At the other end, Noone headed wide from 12 yards out.
Anderson tried his luck from long range again before Tudgay, McCleary and Majewski followed his lead. All of them failed to trouble Casper Ankergren in the Brighton goal.
Buckley, a 76th-minute replacement for Noone, broke the deadlock right at the end when he collected Mackail-Smith's pass 12 yards out and beat Lee Camp at the near post from the angle.