The 20-year-old has had his contract terminated by the club, without playing a game, following an internal investigation after being found guilty of assault.
The case came after a night out to celebrate a not guilty verdict on a separate rape charge ended in him head-butting a woman, but Lenighan kept it from the club when he signed a short-term deal and faked an illness to get out of training on the day of his court appearance.
The Millers immediately suspended him, pending an internal investigation, and following the lengthy process have now decided to terminate his contract.
A club statement read: "Following an internal investigation in to the matters recently in the press and following the reported conduct of the player, Rotherham United can announce that it has terminated the contract of Simon Lenighan.
"The club will be making no further comment on this matter."