Heseltine was born in London in 1916, the son of Philip Heseltine, the composer better known as Peter Warlock, and Minnie Lucy Channing, an occasional model for Augustus John, nicknamed "Puma". He spent most of his childhood In Wales with Warlock's mother and Welsh stepfather at Cefyn Bryntalch and attended Shrewsbury School. This led to the confusion that Nigel himself was Welsh - he was not.
In the 1950s he was based in Rome working as an agronomist for the United Nations Food And Agricultural Organisation. During this time he travelled widely across Africa eventually settling in Madagascar for twelve years and then on Rodriguez Island as Resident Commissioner. Later he wrote several books about Africa, including a classic account of crossing the Sahara - "From Libyan Sands to Chad", and "Madagascar".
Towards the end of his career he was employed by the Department for Aboriginal Affairs in Western Australia travelling extensively in the Outback. He retired in Perth where he died in 1995.