He was born in Donegal, Ireland but raised in the UK. He has joint British/Irish Nationality.

He obtained his BSc in Biochemistry University of London in 1977and his PhD at Imperial College London in 1982. He went on to work on human genetic diseases and then infectious diseases, atSt Mary's Hospital Medical School, London (1982-84) and St George's Hospital Medical School, London (1984-88) and then at the University of Surrey in Guildford, UK.

For more than a decade, McFadden has specialised in examining the genetics of microbes such as the agents of tuberculosis and meningitis and invented a test for the diagnosis of meningitis.

He has published more than 100 articles in scientific journals on subjects as wide-ranging as bacterial genetics, tuberculosis, idiopathic diseases and computer modelling of evolution. He has contributed to more than a dozen books and has edited a book on the genetics of mycobacteria.

He produced a widely reported artificial life computer model which modelled evolution in organisms.

He has lectured extensively in the UK, Europe, the USA and Japan and his work has been featured in radio, television and national newspaper articles particularly for the Guardian. His present post, which he has held since 2001, is Professor of Molecular Genetics at the University of Surrey.

Living in London, he is married and has one son.

McFadden wrote the popular science book, Quantum Evolution on the concept of quantum evolution. The book examines the role of quantum mechanics in life, evolution and consciousness.

McFadden regularly writes articles for The Guardian newspaper in the UK, on topics as varied as quantum mechanics, evolution and genetically modified crops, and has reviewed books there. The Washington Post and Frankfurter Allgemeine Sonntagszeitung have also published articles written by him.