The owner of Candy Crush Saga kicked off a pitch process in March.
The incumbent WCRS held off Bartle Bogle Hegarty, Iris and Leo Burnett to retain its hold on the ad account.
King confirmed the appointment.
WCRS has worked on the business since April 2014, beating Karamarama and then incumbent Albion in a competitive pitch.
Last year, King set up a scented bouncy castle on the South Bank in London to promote its new game Candy Crush Jelly Saga.
A TV spot featured a large mock-up of the game in which the jelly queen character danced off against a woman in rollerskates to Destiny's Child's Bootylicious.
Starcom handles King's media planning and buying.