27 year old King has scored 11 goals so far this term for the Glory Hornet Boys and has joined the Latics after Fulham stalled following a reported failed medical at Craven Cottage.
Speaking about his new addition, Wigan boss Steve Bruce said: "I've been looking to bolster our attacking line up and Marlon certainly fits the bill. He's a proven finisher who provides us with a different kind of goal-scoring threat. He has scored goals at every level he has played at and he is hungry to make an impact in the Premier League again.
"I believe he is the kind of player who could make a real difference to us. He's an aggressive, with great pace and a natural ability to finish, something every manager looks for.
"This is tremendous news for us, especially as there were other clubs in for him. It speaks volumes about the potential there is at this club."
King is ineligible for tomorrow's game with Chelsea but is clear to play in Tuesday's clash with Middlesbrough at the Riverside.
King himself meanwhile said: "I went down [to Fulham], had a long medical and for some reason there was a hitch. I think the two clubs were trying to renegotiate the fee, it had nothing to do with me, but when I picked up the papers I see I had failed a medical!
"I know my body is 110%. I didn't fail a medical. I've been playing for a season and a half now and scoring goals - nothing has changed. As far as I'm concerned and Wigan are concerned, I didn't fail a medical. I had a medical at Wigan and everything went smoothly, so I decided to make the switch.
"I was speaking to Fulham for the last week and a half, I came down to get things sorted out and for whatever reason it didn't happen. Steve Bruce made it clear he wanted me here and I am a Wigan player now."
