Byfuglien got the puck at center ice, skated past Florida defenseman Keaton Ellerby and down the right side, then sent a pass across the crease to a wide-open Ladd for the winning play.
The Thrashers' captain poked it into an empty net, and Atlanta kept its faint playoff hopes alive with a victory.
Ladd also scored in regulation and added an assist while Blake Wheeler found the net twice for Atlanta.
Byfuglien assisted on three scores and Chris Mason turned aside 31-of-34 shots for the victors.
Stephen Weiss and Sergei Samsonov each notched a goal and an assist and Tomas Vokoun made 32 saves for Florida.