"Obviously, we are ecstatic with the results. George Zimmerman was never guilty of anything except protecting himself in self-defense," said his lead attorney Mark O'Mara.
Zimmerman smiled briefly but did not appear emotional as the verdict was read. His family was grinning broadly as they sat behind him in the courtroom.
The family of Trayvon Martin was not present.
Scores of journalists and crowds of demonstrators had gathered outside the courthouse in the dark, awaiting the verdict. Many of the demonstrators were chanting, "no justice, no peace."
Florida Prosecutor Angela Corey argued that the tragic case was a test of Florida's gun laws as well as social boundaries.
"This case has never been about race, nor has it ever been about the right to bear arms," Corey said. "But Trayvon Martin was profiled. There is no doubt that he was profiled to be a criminal. And if race was one of the aspects in George Zimmerman's mind, then we believe that we put out the proof necessary to show that Zimmerman did profile Trayvon Martin.
"But the right to bear arms is a right in which we all believe. I especially believe in that will right. What we want is responsible use when someone feels they have to use a gun to take a life," Corey added, saying: "They have to be responsible in their use, and we believe that this case all along was about boundaries."
The jury had deliberated for more than 16 hours since Friday in the case.
Zimmerman, 29, had been accused of pursuing Martin through a gated community in Sanford, Florida and shooting him during an altercation.
Defense lawyers insisted Zimmerman acted in self-defense after Martin, 17, wrestled him to the ground and started bashing his head into the pavement.
Zimmerman faced possible life in prison if convicted of second-degree murder. The jury was also instructed to consider an alternate charge of manslaughter, which carries up to a 30-year sentence.
"Mr. Zimmerman, I have signed the judgment that confirms the jury's verdict. Your bond will be released. Your GPS monitor will be cut off when you exit the courtroom over here. And you have no further business with the court," Judge Deborah Nelson said shortly after the decision was read.
The February 2012 killing ignited widespread controversy after police initially declined to press charges against Zimmerman.
Community leaders on Friday had called for calm regardless of the eventual verdict.
"If Zimmerman is convicted, there should not be inappropriate celebrations, because a young man lost his life," Reverend Jesse Jackson, a veteran civil rights activist, said.
"If he is not convicted, we should avoid violence because it will only lead to more tragedies."