Treasure, who had been ill for some time, was regarded as one of UK advertising's most important and influential figures during the 60s and 70s and an outstanding problem-solver.
Despite tumbling into the business almost by accident, he not only led JWT during a time that saw a four-fold billings growth, but also served as the IPA president and as the vice-chairman of Saatchi & Saatchi.
The holder of a PhD in economics from Cambridge and a one-time economics lecturer, Treasure was famous for bringing an academic approach to advertising and for his analytical and incisive mind.
Treasure's entry to advertising was via the British Market Research Bureau, then a JWT subsidiary, which he joined in 1952. Five years later, he was the managing director before switching to JWT in 1960 as the director of research and marketing.
With no great ability for day-to-day management, Treasure's real talent was in dealing with clients who regarded him more as a management consultant.
"He wasn't an advertising man born and bred," Stephen King, JWT's former planning chief once said of him. "He could look at things with the view of someone who had matured outside advertising."
Treasure's career also embraced spells as the chairman of Taylor Nelson AGB, the dean of the City University Business School, the president of the Market Research Society and the president of Nabs, the industry charity.
He also served as a director of Rowntree Mackintosh, a JWT client.
Hamish Pringle, the IPA director-general, said: "With John's passing we have lost another giant of UK advertising. His contribution to the industry was enormous."
A memorial service for Treasure will be held at St Bride's Church, Fleet Street, on 12 May at 2pm.