Kopecky had been acquired from Chicago on June 27 in exchange for the Panthers' seventh-round pick in the just-completed Entry Draft. He would have become an unrestricted free agent had he not signed by July 1.
"Tomas is a proven winner who we are pleased to have signed," Florida GM Dale Tallon said in a statement. "He is a hard-working player who is tough to play against and recorded career highs in both goals and assists last season. He is a versatile player who can play any forward position, has good vision at both ends of the ice and will immediately make an impact in our lineup."
Kopecky, who won the Cup with Detroit in 2008 and Chicago in 2010, had 15 goals and 27 assists in 81 games with the Blackhawks last season. In 338 NHL games, he has 37 goals and 58 assists, plus 4 goals and 3 assists in 30 playoff games.