Wilson was acquitted of raping another 17-year-old girl at the party.
The 1995 law Wilson violated was changed in 2006 to make oral sex between teens close in age a misdemeanor, similar to the law regarding teen sexual intercourse. But the state Supreme Court later upheld a lower court's ruling which said that the 2006 law could not be applied retroactively.
Chief Justice Leah Ward Sears wrote in the majority opinion that the changes in the law "represent a seismic shift in the legislature's view of the gravity of oral sex between two willing teenage participants."
Sears wrote that the severe punishment makes "no measurable contribution to acceptable goals of punishment" and that Wilson's crime did not rise to the "level of adults who prey on children."
The state Supreme Court had turned down Wilson's appeal of his conviction and sentence, but the justices agreed to hear the state's appeal of a Monroe County judge's decision to reduce Wilson's sentence to 12 months and free him. That judge had called the 10-year sentence a "grave miscarriage of justice."
Dissenting justices wrote that the state Legislature expressly stated that the 2006 change in the law was not intended to affect any crime prior to that date.
They said Wilson's sentence could not be cruel and unusual because the state Legislature decided that Wilson could not benefit from subsequent laws reducing the severity of the crime from a felony to a misdemeanor.
They called the decision an "unprecedented disregard for the General Assembly's constitutional authority."
A spokeswoman for Wilson's lawyer said his legal team received no advance notice of the decision.