The chairman role will not formally be filled after his departure from the Creston-owned agency.
Bostock founded Nelson Bostock with Roger Nelson in 1987 as a consumer tech and telecoms agency, and over the years it has expanded into a multi-faceted operation that includes consumer agency Fever, digital and social engagement agency Things Unlimited and content creation agency MediaWorks. The group also includes its b2b and corporate agency Nelson Bostock Unlimited.
In 2003 Nelson and Bostock sold the business to Creston, where Bostock subsequently joined the executive board. Nelson retired in 2007, returning to his native New York.
Bostock became non-executive chairman in 2013, allowing him to dedicate more time to other interests including a non-executive directorship within the NHS and charitable work with the Citizenship Foundation, which he chairs.
Key Nelson Bostock Group Unlimited clients include Canon, EE, HTC, Now TV, Sky, Sony PlayStation, TelecityGroup, Toshiba and Warner Bros.
Bostock said: "When I look at our client list today, at the groundbreaking work the agencies produce, at the awards we’ve won and at the talent of the people within the group, I find it hard to reconcile with the memory of Roger and me setting up with an Amstrad word processor and a fax machine in an attic on the Portobello Road."
He added: "I’m incredibly lucky to have been supported by a formidable leadership team under group CEO Lee Nugent, with outstanding board of colleagues including Bruce McLachlan and Frankie Oliver [joint MDs of Fever], and Nick Clark [MD of Nelson Bostock Unlimited].
"Without them I would never have had the luxury of pursuing the other interests that are important in my life.
"I feel very comfortable that the time is right – both for me and for the business – to make way for the next generation of management to continue to take the business forward to even greater heights."
Nugent said: "Though it’s terrifically sad for us that Martin has chosen this year to retire, he steps down with our love, appreciation and admiration. He will be missed both professionally and personally, not least by me.
"He’s been a terrific coach and mentor and remains a great friend. Even though he won’t be physically ‘inside’ the organisation any more, Martin’s spirit, personality and relentless command of great grammar will remain imprinted on the group forever.
"I’m proud to have been given the opportunity to lead a business that continues to bear both his and Roger Nelson’s names."
Bostock also chaired the PRCA Council in 2013-14.