The announcement comes two days after it was revealed Richardson is under internal investigation over "allegations of workplace misconduct," according to a statement released by the Panthers on Friday.
"I believe it is time to turn the franchise over to new ownership," Richardson wrote in his five-paragraph letter announcing his intention to sell the team, which was published Sunday on the Panthers' website and shared on Twitter. The statement does not address the allegations against him.
In the statement Friday announcing the investigation, Panthers spokesman Steven Drummond said: "The Carolina Panthers and Mr. Richardson take these allegations very seriously and are fully committed to a full investigation and taking appropriate steps to address and remediate any misconduct.
"The entire organization is fully committed to ensuring a safe, comfortable and diverse work environment where all individuals, regardless of sex, race, color, religion, gender, or sexual identity or orientation, are treated fairly and equally," the statement continued.
The NFL on Sunday said it would be taking over the investigation. Drummond told The Associated Press that the team had asked for the league to take over the investigation.
"We thought it would be best for transparency reasons," he said.
The Panthers statement doesn't give specifics on the allegations against Richardson, citing the ongoing nature of the investigation.
A former player with the Baltimore Colts, Richardson was awarded an expansion franchise by the NFL in 1993. He has been the team's only owner. In his statement, Richardson said he would not begin the sale process or entertain inquiries until the final game of the current season is played.
The Panthers have never won a Super Bowl.