Three black men falsely accused and convicted of raping two white women in Alabama have received posthumous pardons, more than 80 years after their arrests.

Haywood Patterson, Charles Weems and Andy Wright were among nine teenagers, dubbed The Scottsboro Boys, who were convicted by all-white juries in 1931, in a case which came to symbolise racial injustice in the US.

All but one were sentenced to death.

It is a great day for freedom. Sheila Washington, Scottsboro Boys Museum

"Today, the Scottsboro Boys have finally received justice," Robert Bentley, governor of Alabama, said.

Five of the men's convictions were overturned in 1937 after one of the alleged victims recanted her story.

One defendant, Clarence Norris, received a pardon before his death in 1976. State law at the time did not permit posthumous pardons - a situation which lasted until April 2013, when Republican state Senator Arthur Orr spearheaded a change in the law.

"It is a promising reminder of how far we have come as a state since those regretful days in our past," he said following the pardons issued by the state parole board on Thursday.

The founder of the Scottsboro Boys Museum, Shelia Washington, said the pardons "give the history books a new ending - 'not guilty'".

The case helped bring about the US civil rights movement, and inspired songs, books and films. A Broadway musical was staged in 2010, the same year the museum opened in Scottsboro.

Their appeals resulted in US Supreme Court rulings that criminal defendants are entitled to effective counsel and that black people could not be systematically excluded from criminal juries.

"They didn't know how much they meant in history while they were alive," said Washington. "It is a great day for freedom."