McKeown, who joined Dare in June last year from RKCR/Y&R, left the agency on Friday 26 April.
Incoming Dare chief executive, Leigh Thomas, who starts tomorrow, will be tasked with appointing a new chief planner.
The former Dare chief strategy officer Andy Nairn hired McKeown to lead the agency's planning department in June 2012. Nairn left the agency in August that year and McKeown has been the most senior planning executive at the company since then.
Prior to joining Dare, McKeown was board account planning director at RKCR/Y&R for two years working with clients including LG Electronics, Land Rover and Vodafone.
Previously, he worked as a planning director working in freelance and permanent positions at agencies including DDB (now Adam&Eve/DDB), Beattie McGuinness Bungay, Leo Burnett and Wieden+Kennedy.
McKeown started his career in ad sales, before moving to Blue Source Creative Communications (the specialist youth marketing arm of Blue Source Design), and then PHD.