Donald Trump pardoned convicted boxing champion after Rocky star Sylvester Stallone personally intervened

Donald Trump has praised the role Sylvester Stallone has played in a pardon being issued to one of the greatest boxers of all time.

Jack Johnson became the first black heavyweight champion of the world when he won the title in 1908 and the pugilist from Galveston, Texas, became one of the most revered fighters in boxing history, despite facing racism and prejudice during the Jim Crow era in the United States.

The posthumous pardon was granted after Johnson was convicted by an all-white jury of accompanying his white girlfriend across state lines for 'immoral purposes' more than 100 years ago.

"I believe that Jack Johnson a worthy person," Trump said during a press event in the Oval Office that also featured British boxing great Lennox Lewis. "So I am taking this very righteous step, I believe, to correct a wrong.

Jack Johnson, boxing's first black heavyweight champion (Getty)

"We righted a wrong ... And a lot of people knew it. I knew it."

And Trump had previously confirmed via social media that Stallone, who was another attendee of the Oval Office event, had been a key driver in the campaign to get Johnson's name cleared.

"Sylvester Stallone called me with the story of heavyweight boxing champion Jack Johnson," he tweeted.

"His trials and tribulations were great, his life complex and controversial. Others have looked at this over the years, most thought it would be done, but yes, I am considering a Full Pardon!"

Senator and former presidential candidate John McCain also backed up calls for Johnson to receive a posthumous pardon.

"Jack Johnson was a boxing legend and pioneer whose career and reputation were ruined by a racially charged conviction more than a century ago," McCain, who had been in support of the pardon since 2004, said in a statement.

"Johnson's imprisonment forced him into the shadows of bigotry and prejudice, and continues to stand as a stain on our national honour."

Johnson's great-great niece, Linda Haywood, had long campaigned for the boxing legend to be pardoned, too.

"I certainly hope President Trump will grant my uncle a pardon. This pardon is long overdue and I was very disappointed when President Obama did not grant my uncle a pardon," Haywood said.

"Knowing that he was treated unfairly and unfairly convicted and targeted because of his choice of companions, who happened to be Caucasian, that's wrong.

"It bothered my people to the point they didn't even want to talk about it. My mother didn't even want to talk about it. That's stupid ... It bothers me.

"The last thing you want to do is die and have your name tarnished. That's wrong. You don't want it to be tarnished if you're living."

Johnson, who died in 1946, is remembered as one of the greatest boxers of all time.