The rapper was murdered by a jealous ex-girlfriend in 1996, in what prosecutors say was a self-defense attempt.
Tupac was convicted of murder in 1995 and sentenced to life in prison.
But in April 2016, the U.S. Supreme Court ruled in his favor, saying a jury would have to consider the facts of the case before convicting him.
The justices also said it would be up to prosecutors to prove the death was an accident.
Tupamania was born Tupac Amaru Shakur, but his real name was Charles “Phenomenon” Tupac.
In 1971, Tupac’s mother, Dolly Parton, was raped and killed in her home by her boyfriend, actor Michael Jackson.
She later wrote an autobiography, which became a best-seller and won her a Grammy award.
She died in 1988.
On the night Tupac died, he had a violent argument with a girlfriend, then called her the “mother f—— n—a” on tape.
He was sentenced to 35 years in prison and received a three-year, 50-percent chance of parole in 2018.
On Wednesday, the Associated Press reported that prosecutors had agreed to drop a murder charge in the case.
Prosecutors had argued that the evidence in the trial was insufficient and that a jury could not be sure of the facts.
But Justice Anthony Kennedy ruled that the prosecution’s evidence was sufficient and that it was “beyond a reasonable doubt” that Tupac killed his ex-wife and that she killed herself.
“The evidence is sufficient to conclude that this was an act of self-defence,” Kennedy wrote in the opinion.
“I do not believe that a juror would be barred from considering the evidence if it were not sufficient to reach that conclusion.”
On Wednesday night, Tupamanyas widow, Donda, released a statement through her attorneys, saying, “It is with great sadness that I must inform you that I have been diagnosed with cancer.
I am fully and completely cooperating with all efforts to help me through this devastating and difficult time.”
She also said the family is considering filing a civil rights lawsuit against the state.
The Associated Press contributed to this report.