Andrew Harrison, chief executive of the RadioCentre, the trade body for the commercial radio industry, will extend his role and take over as chairman of the RAB from 1 January. King has held the post for the last two years.
Seven people across the company have taken voluntary redundancy following an internal cost-cutting process, which took place during November, prompted by the economic slowdown.
One member of staff has left the RAB and the rest came from the RadioCentre. The job cuts reduce the RadioCentre's headcount from 35 to 28.
A RadioCentre spokesperson said: "RadioCentre can confirm that a small number of staff have left the organisation having taken voluntary redundancy.
"RadioCentre continues to have a critical industry role especially in marketing our medium to advertisers, clearing advertisements and being the voice of Commercial Radio in our external relations with government, regulators and other stakeholders.
"However, it is right that RadioCentre should adapt itself to the changing needs of the industry it represents."
Paul Brown is stepping down as non-executive chairman of the RadioCentre at the end of the year and Dianne Thompson, chief executive of Camelot, will be the next non-executive chairman from February.