The club announced on Friday night that his year in charge has come to an end.
Under King the Wings made the National League South Promotion Final - losing narrowly to runners-up Woking.
But he won’t be around next season to try and go one better.
Chairman Mark Goldberg said: “On behalf of the board, our staff, players and all Wings fans I would like to place on record our thanks to Steve on a fantastic season which saw us win the London Senior Cup for the first time in 29 years and the team just 90 minutes away from achieving promotion to the Vanarama National League.
“Steve leaves with the best wishes of all of us at Welling United and he will always be warmly welcomed at Park View Road.”
King said in a statement on the club’s website: “I am incredibly proud of what we and players achieved last season but now is the right time for myself and the club to take a different path.
“I’ve had a great time at the football club and we very nearly pulled off the unthinkable. I wish the club every success in the future especially the fans who were fantastic with me from day one”.