Hilary Crampton Walton, née Pym, was born in Oswestry in 1916, the second daughter of Frederic Crampton Pym (1879–1966), solicitor, and his wife, Irena Spenser, née Thomas (1886–1945). Like her elder sister, the novelist Barbara Pym (1913-1980), Hilary attended The Liverpool College for Girls, Huyton [later Huyton College, Liverpool]. Hilary also followed Barbara to Oxford and studied Classics at Lady Margaret Hall, University of Oxford.

After Oxford, Hilary took a secretarial course in London and began work for the BBC in 1938: the sisters lodged together in London. In 1940, Hilary was transferrred with the BBC to Bristol and was joined in 1941 by Barbara. They lived at The Coppice, along with Honor Wyatt, her children, and one other family.

On 26th August 1942, Hilary married Alexander Crawford Wellesley Walton (known as Sandy). In 1944, Hilary joined the BBC's Gramophone Department and lived in London whilst her husband was abroad with the RAF. In 1946, after Sandy had returned to England, the couple decided to separate and officially divorced in 1949.

After separating from Sandy, Hilary lived in London with Barbara. She retired from the BBC in 1971 and the following year bought Barn Cottage, Finstock near Oxford. Barbara died in 1980 and Hilary became a careful custodian of Barbara's memory, ensuring that interest in her works continued. Hilary died in 2004.

For a full biography of Barbara Pym, see The Oxford Dictionary of National Biography.