The Philadelphia rapper Meek Mill, who has become a symbol of criminal justice reform, as well as an outspoken advocate, pleaded guilty on Tuesday to a misdemeanor gun charge stemming from a 2007 arrest, ending a legal saga that has sent him to prison multiple times during more than a decade of probation and appeals.

Meek Mill, born Robert Rihmeek Williams, will not serve any additional prison time and will no longer be on probation, said his lawyer, Joe Tacopina, in an interview.

“What happens now is he begins his life,” Mr. Tacopina said. “For the first time since he was a teenager, he’s not under probation, he’s not under any supervision. It’s the first time in his adult life that he’ll be able to go somewhere without asking permission.”

The guilty plea to a misdemeanor charge — possession of a firearm — came after a Pennsylvania appeals court ruled in July that Mr. Williams would be granted a new trial and a new judge, overturning his 2008 conviction. Prosecutors for the district attorney’s office had backed Mr. Williams’s requests, telling the court that the office could no longer call its lone witness in the case, a Philadelphia police officer who had been found guilty by the department of lying and theft.