On Thursday, California Gov. Jerry Brown granted Robert Downey Jr. a full and unconditional pardon for his time in jail for drug offenses in the late 1990s.

Mr. Downey, who has been one of Hollywood’s biggest stars since his comeback in 2008’s “Iron Man,” was one of 91 individuals given pardons on Thursday by California Governor Jerry Brown, who has made it a Christmas Eve ritual to award pardons.

The hundreds of pardons Brown has issued in each of his four terms are typical, except for his three immediate predecessors. Arnold Schwarzenegger, a Republican, granted 15, Gray Davis, a Democrat, granted none, and Republican Pete Wilson, a Republican, granted 13.

The order states: “By completion of his sentence and good conduct in the community of his residence since his release, Robert John Downey, Jr. has paid his debt to society and earned a full and unconditional pardon.”

According to Brown’s website, the pardon does not erase a conviction, but it does restore voting rights and is a public declaration that the individual has stayed out of trouble and exhibited “exemplary behavior.”

In California, those who have been convicted of a crime can petition to the governor for a pardon. According to the governor’s office, applicants must get a court decree proclaiming rehabilitation and demonstrate that they have led “productive and law-abiding lives following their conviction.”

Earlier this year, Mr. Downey filed a judge’s certificate of rehabilitation. According to the pardon, Mr. Downey “has lived an honest and upright life, exhibited good moral character, and conducted himself as a law-abiding citizen.”

“You’re only on the naughty list if you get caught…” Mr. Downey tweeted before the pardon was issued on Thursday.

Mr. Downey, 50, was arrested in 1996 on narcotics and weapons charges after police discovered an unloaded .357 Magnum in his car, as well as minor amounts of heroin and cocaine. In 1999, he was sentenced to prison after several probation breaches.

He completed his parole in 2002 and went on to star as Tony Stark in the Iron Man franchise, becoming the highest-paid actor in Hollywood in 2015, with an estimated income of $80 million.

Downey has played Iron Man in Disney’s blockbuster blockbusters since 2008, including The Avengers, which is based on the Marvel comic books.

Mr. Downey’s problems persisted after his release, and by 2003, he was regarded uninsurable as an actor and had difficulties obtaining employment. However, he told David Carr of The New York Times that one day that year, he dumped all of his drugs into the ocean and declared he was “done.”

The 50-year-old actor has been nominated for two Academy Awards, for his roles in Chaplin (1992) and Tropic Thunder (2008).

Mr. Downey stormed out of a British television interview in April as the questioning went to his drug and alcohol problems. In a 2008 interview with Mr. Carr, he again dodged inquiries about his history.

“If I see somebody who is throwing their life away with both hands and is raging around and destroying their family, I can’t understand that person,” he said. “I’m not in that sphere of activity anymore.”