On July 1, 2009, Kopecký signed a two-year deal with the Chicago Blackhawks worth $1.2 million per season. He played in 74 games for the Blackhawks in his first year with the team, posting 21 points, 28 penalties-in-minutes (PIM), two game-winning goals and a shooting percentage of 10.5%. Into the post-season, Kopecký was a regular starter on Chicago's third or fourth forward lines. He scored a crucial goal to put Chicago up by two in the Western Semifinals against the Vancouver Canucks, but his most crucial would be in his first game back in the lineup after being a healthy scratch for all four games of the sweep of the San Jose Sharks. Replacing the injured Andrew Ladd, Kopecký netted the 6–5 game-winning goal in the Game 1 victory of the 2010 Stanley Cup Finals. Ladd returned the next game, but Blackhawks Head Coach Joel Quenneville kept Kopecký in the lineup to play every game of the six-game series. He finished the playoffs with solid statistics; in 17 games, he tallied six points, 8 PIM, one game-winning goal and a shooting percentage of 14.3%. On June 9, 2010, at the age of 28, he won the Stanley Cup with the Blackhawks and hoisted the Cup for the second time in his life.