[5] Early in the 1950s, he undertook National Service with the King's African Rifles in Kenya.
In 1963, Wallace was among a party of birders,[7] led by Guy Mountfort[8] and including Julian Huxley,[8] George Shannon[7] and, James Ferguson-Lees,[7] that made the first ornithological expedition to Azraq in Jordan.
[7] The expedition's recommendations eventually led to the creation of the Azraq Wetland Reserve and other protected areas.
[12] Wallace appeared as a guest on BBC Radio 4's Saving Species, discussing his October 1960 observations of the visible migration of birds over London, on their 50th anniversary.
[13] He was described as "one of the very top ornithologists in the UK",[14] "one of the great names of British bird-watching",[15] by the BBC as "a pioneer of ornithology [in the United Kingdom]",[13] and by Mark Cocker as both "one of the godfathers of modern birding"[4] and "the grand old man of birds".