Joe Biden is to pardon thousands of Americans convicted of possessing cannabis.
The US president said those with federal convictions for "simple possession" could be "denied employment, housing, or educational opportunities as a result".
He added: "My pardon will remove this burden on them."
In a White House video, the president said he was concerned about racial disparities, too.
"While white and black and brown people use marijuana at similar rates, black and brown people are arrested, prosecuted and convicted at disproportionately higher rates," he said.
Those benefitting from the policy will receive a certificate of pardon, which they can show to potential employers.
The Department of Justice said it would begin the process of providing those certificates "in coming days".
The vast majority of cases of cannabis possession are at state level, and Mr Biden is calling on governors to follow his lead.
The president said "important limitations on trafficking, marketing and underage sales should stay in place".
Non-citizens who were in the US illegally at the time of their arrest will not be pardoned.
Currently, cannabis is classified as a schedule one substance in the US, "the same as heroin and LSD, and more serious than fentanyl", the president said.
"It makes no sense," he commented. He has announced a review of how cannabis is scheduled under federal law.
According to the White House, no one is currently in federal prison solely for "simple possession" of the drug.
Kassandra Frederique, executive director of the Drug Policy Alliance, said her organisation was "thrilled" by Mr Biden's announcement.
"This is incredibly long overdue," she said. "There is no reason that people should be saddled with a criminal record, preventing them from obtaining employment, housing, and countless other opportunities, for something that is already legal in 19 states and DC and decriminalised in 31 states."
In the video, the president said he believed that "no one should be in jail just for using or possessing marijuana".
He added: "It's already legal in many states. Too many lives have been upended because of our failed approach to marijuana.
"It's time that we right these wrongs."