A graduate of the Royal College of Art, Holtom was a conscientious objector in World War II. On 21 February 1958 he designed the Nuclear Disarmament logo for the first Aldermaston March, organised by the Direct Action Committee against Nuclear War, Easter 1958 (4-7 April). The logo was not copyrighted, and was available for use by the Campaign for Nuclear Disarmament, also founded in 1958; it later became known in the wider world as a general-purpose peace symbol. The design was a combination of the letters "N" (two arms outstretched pointing down at 45 degreess) and "D" (one arm upraised above the head) of the flag semaphore alphabet, standing for nuclear disarmament.
It was at the Peace News office at 5 Caledonian Road, London. N.1. (above Housmans Bookshop) that the CND (peace symbol) was adopted.
Holtom died at the age of 71. His daughter Anna Scott is an artist.