Harold Sumption (26 November 1916 - 18 March 1998) was an English advertising executive and fundraiser. He was associated with charities including Oxfam, Help the Aged and ActionAid, as well as co-founding the International Fundraising Workshop (IFRW).

A committed Quaker, Sumption served as Oxfam's unpaid advertising adviser from the late 1940s until the late 1980s, and his advice was instrumental in making Oxfam the largest charity in the UK. His work for Oxfam and other charities, as well as his innovations in direct marketing, led to him being described variously as "the father of modern-day fundraising", the "inventor of Marketing 1.0" and the "shy pioneer" who was "the biggest influence on a generation of British fundraisers".

Born in Culmstock, the son of a Devon farmer, Harold Sumption moved to London in the early 1930s to an apprenticeship at an advertising agency. He became a Quaker after accidentally finding himself at the Yearly Meeting at Friends House, thinking that he was attending a talk by Jomo Kenyatta.

In 1938 he married Ruth Burrows at the Friends meeting house in Wellington, Somerset. In the early 1940s they had two children, Jennifer and Adrian.

During the Second World War, he was a conscientious objector, and suffered a severe return of the tuberculosis that had infected him before the war. In 1946, after 18 months in bed, he undertook his first fundraising assignment: to raise the money to fund his own treatment in a sanatorium in the Swiss Alps. He proposed to the fledgling NHS that they pay towards this treatment whatever it would cost to treat him in London, as this would both free up a bed and in all likelihood lead to an earlier recovery. They accepted this proposal, which covered 33% of the sanatorium costs. The remainder he secured from the Queen Alexandra Sanatorium Fund and the National Advertising Benevolent Society.

It was this fundraising experience, and his Quaker faith, which, following his recovery, led him to place an advertisement in the Quaker journal The Friend seeking a charity to which he could contribute his advertising experience. Cecil Jackson-Cole, of the small young charity then known as the Oxford Committee for Famine Relief, replied. Sumption advised Oxfam for the next 35 years, serving as advertiser, council member, and board member, although he was never on the organisation's payroll.

Alongside his unpaid role as adviser to numerous charities, Sumption had a successful career in advertising. He formed the first British direct marketing division, at NW Ayer and worked at fashionable 1970s start-up MWK. He was a fellow and council-member of the Institute of Practitioners in Advertising, and helped set up the Montreux International Direct Marketing Symposium. He was also one of the first two honorary fellows of the UK's Institute of Charity Fundraising Managers.

Sumption's fundraising was informed by the belief that every person has a Good Samaritan within them, but that they need to be shown with clarity, honesty and urgency how and why to exercise that Samaritan instinct.