Hayes was born in Harrow, Middlesex, the eldest child of lithographer Walter Leopold Hayes and Hilda Beatrice Fisher. He won a scholarship to Hampton School and served in the Royal Air Force as a cadet pilot before entering journalism after World War II. His family connection to the printing trade gave him early access to Fleet Street networks, and he worked his way through local, regional, and national journalism. Hayes became associate editor of the Daily Mail and in 1956, at the age of 32, the last editor of the Sunday Dispatch. It was during this period that he met Colin Chapman, founder of Lotus Cars, who became an occasional contributor to the motoring column.
In January 1962 Hayes crossed from journalism to industry, accepting the role of head of public relations at Ford UK. Ford's product range at the time — dependable cars such as the Cortina and Zodiac — had little sporting image. Hayes concluded that a decisive push into competition was essential to transform perceptions, and he quickly initiated Ford's first motor sport activities. Under the campaign brand "Total Performance," Ford's public profile shifted from that of a conservative mass manufacturer to one associated with speed and performance.
One of his first major moves was to sign a relatively unknown Scottish racing driver, Jackie Stewart, who was attending the 1964 British International Motor Show at Earl's Court. Hayes offered Stewart £500 to promote Ford products in 1965 along with the use of a Ford Zodiac. Stewart later reflected: "I didn't know who Walter Hayes was, but I did know that to have a contract with Ford Motor Company was a big deal." The relationship lasted forty years.
When Ferrari rejected a proposed Ford takeover, Hayes became part of the team backing Henry Ford II's ambition to challenge Ferrari on the racetrack. Hayes initiated discussions with Cooper, which did not bear fruit, but agreements with Lotus produced a successful Indianapolis 500 programme, and an arrangement with Lola produced the prototypes for the Ford GT40 — the car that broke Ferrari's dominance at Le Mans.
Hayes's most enduring contribution to motorsport was the funding and facilitation of the Cosworth DFV V8 Formula One engine. Colin Chapman approached Ford after Coventry Climax decided not to develop a large-capacity engine for the new three-litre Formula One regulations introduced in 1966. Chapman had already spoken with Keith Duckworth, who estimated that a competitive three-litre engine could be built for £100,000.
Hayes arranged a dinner between Chapman and Harley Copp, an American engineer who had managed Ford's successful NASCAR programme in the 1950s. Together Hayes and Copp developed a business plan: stage one would produce a four-cylinder twin-cam engine for Formula Two; stage two, completed by May 1967, would deliver a V8 for Formula One. In return, Chapman would engineer specials for Ford, beginning with the Lotus Cortina.
The Cosworth DFV won on its competitive debut at the 1967 Dutch Grand Prix, driven by Jim Clark in a Lotus 49. Hayes subsequently decided that wider availability of the engine would serve Ford's interests better than exclusivity, and he arranged for the DFV to be supplied to other teams. The engine went on to power world champions Graham Hill, Jackie Stewart, Jochen Rindt, Emerson Fittipaldi, James Hunt, Mario Andretti, Alan Jones, Nelson Piquet, and Keke Rosberg, and brought titles to teams including Lotus, Matra, Tyrrell, McLaren, and Williams. Its 155th victory came at the 1983 Detroit Grand Prix, sixteen years after its debut.
Hayes joined the board of Ford of Europe at its founding in 1967, was made a vice-president of Ford's American parent company in 1980 under chairman Philip Caldwell, and was appointed CBE for services to the motor industry in 1982. He returned to Britain as vice-chairman of Ford of Europe and was instrumental in establishing the Premier Automotive Group in 1989, overseeing Ford's acquisitions of stakes in Aston Martin and ultimately Jaguar Cars. Hayes played a direct role in the creation of the DB7, recognising Aston Martin's need for a higher-volume model and guiding the project through to production. He retired from Ford of Europe in December 1989 but continued his involvement with Aston Martin through the early 1990s.
Walter Hayes died on 26 December 2000. Jackie Stewart described him as "always a gentleman of great dignity and style" with "tremendous peripheral vision." Stuart Turner, who had also moved from journalism to the motor industry, called him "the greatest public relations officer that the motor industry has ever had." Hayes's willingness to back the Cosworth DFV project — which he described as hanging his career "on the line" — proved one of the most consequential single investments in the history of Formula One.