King was sent to prison for an incident in a London nightclub in December when, while he was on loan to Wigan's Premier League rivals Hull, he groped a young woman and then broke her nose after she spurned his advances.
King, a striker with north-west side Wigan, was convicted of sexually assaulting a 20-year-old university student and causing actual bodily harm.
Wigan chairman Dave Whelan told Sky Sports that King would be sacked after a mandatory notice period had expired.
"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," Whelan said.
"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."
The court heard how King, 29, was celebrating his wife's pregnancy and scoring a winning goal hours earlier.
After he was repeatedly "cold-shouldered" by women in the bar, he lost his temper with the victim and in an outburst of "completely gratuitous violence" lashed out at her, "smashing" her to the floor, the court heard.
He had denied the charges, claiming he was a victim of mistaken identity.