The 29-year-old has been punished for punching a student in the face in the Revue Bar in Soho last December.
King had insisted that he was the victim of mistaken identity, but the jury decided that the footballer was the perpetrator of the attack, while he was also found guilty of sexual assault.
Latics chairman Dave Whelan confirmed on hearing the verdict that King will be sacked by the Premier League club.
He told Sky Sports News: "We have to follow the rules and regulations, which means we will have to give him 40 days' notice that his contract will be cancelled.
"He is absolutely sacked - we will not tolerate football players who get sent to jail for 18 months.
"As far as we are concerned, he is finished with football at Wigan Athletic."
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