The jurors acquitted Zimmerman of second-degree murder and manslaughter, The Washington Post reported.
Zimmerman admitted to killing the 17-year-old boy as he walked through a gated community in Sanford, Fla., to his father’s home last February.
The 29-year-old neighborhood watchman suspected Martin was a criminal when he confronted him that night.
They struggled, and Zimmerman shot Martin. He claimed self-defense under Florida’s “stand your ground law.”
But Martin, an African-American, was unarmed and held little more than his cellphone, soda and candy from the store.
Zimmerman wasn’t immediately charged, which sparked protests across the country, even prompting President Barack Obama to say if he had a son, he’d “look like Trayvon.”
Just hours before reaching a verdict on Saturday night, the jury broke to ask a question about manslaughter, The New York Times said.
It was their second day of deliberation, and they’ve decided unanimously that Zimmerman acted in self-defense.
About 350 gathered outside the courthouse shouting "the system has failed," and "justice for Trayvon."
Most were Martin supporters who expressed disbelief.
"How is the law different for one and not for the other? Trayvon was standing his ground when Zimmerman came and messed with him, a young man coming from the store," said bystander Nina Mays.
And despite some close calls (and insults and slurs tossed both ways) nothing amounted from the tension earlier in the day.
One Zimmerman supporter shouted "go get your welfare checks, go get your crack" toward the Martin camp.
Yet, there was those who took a more dignified approach, saying Zimmerman was covered by the "stand your ground" law.
Legal experts agreed, and told the Miami Herald that prosecutors failed to make their case.
Jude M. Faccidomo, former Florida Association of Criminal Defense Lawyers president, said the jury identified with the "right to defend yourself."
"Especially when cases are so gray, like this one was, self-defense really resonates because people can associate with being afraid, Faccidomo told the Herald.