The 30-year-old rapper, whose real name is Clifford Harris Jr., was on supervised release for federal weapons charges when he was arrested Sept. 1. A judge earlier this month sentenced him to 11 months in prison.
The deputy district attorney who rejected the case cited the sentence and the small amount of drugs found as reasons charges aren't being pursued.
"The Los Angeles District Attorney's Office's decision to reject TI's case was the right thing to do under the circumstances," said Harris' attorney, Steve Sadow.
T.I. is expected to begin his prison term on Nov. 1.
The Associated Press contributed to this report.