[3][4] He qualified as an editor and worked for several years writing academic texts before concentrating in the wildlife field guides that he has made since 2008.
[5][4][6] McMullan has specialised in making nature guidebooks for the most diverse countries of tropical South American countries[3] including Venezuela, Colombia and Ecuador, where he has also worked as a naturalist guide, birding tourguide and author.
[26][27] His illustrations have appeared in several other books, articles, publications, including forming part of the natural history collection of the Luis Angel Arango Library of the National Bank of Colombia.
[4][25][32] He is involved with indigenous communities such as the Awá of southwestern Colombia and the conservation of their lands[4] and is an active campaigner and donor in the battle to combat climate change.
[33] He is a regular speaker at birding and conservation fairs and conferences,[34][35][36] occasional exhibitor of his paintings[37] and has appeared on television programs broadcast in UK, Spain,[38] Australia and Colombia, where programs have been made exclusively about his work.