JACKSONVILLE, Fla. — A Florida man who shot an unarmed teenager to death during a dispute over loud music was convicted of first-degree murder on Wednesday after a jury rejected his claim that he fired his gun repeatedly in self-defense.

Under Florida law, the man, Michael Dunn, 47, will spend the rest of his life in prison, without the possibility of parole.

This was the second time that Mr. Dunn, a software developer, had faced a jury in the death of Jordan Davis, 17, a high school junior who was killed as he sat in a friend’s car in a convenience store parking lot. In February, Mr. Dunn was convicted of three counts of second-degree attempted murder — one for each of the surviving teenagers who were with Mr. Davis — and of firing deadly missiles.

But that jury could not unanimously agree whether Mr. Dunn killed Mr. Davis in self-defense or, as prosecutors argued, in a fit of rage on Nov. 23, 2012. Mr. Dunn had said that Mr. Davis, who sat in a Dodge Durango parked next to Mr. Dunn’s car, pointed a shotgun in his direction and tried to get out of the car with it. The police never found a firearm and witnesses never saw one.