Fincham was appointed first as lecturer in botany (1950–1954) and then as reader (1954–1960) at University of Leicester. A year as an Associate Professor in the Massachusetts Institute of Technology preceded his appointment as Head of the Genetics Division of the John Innes Centre (JIC) in 1961. Fincham’s appointment at the JIC is an acknowledgement that much really progressive work in biology is now done with microrganisms and is a strategic move by K.S. Dodds to give JIC leadership in the field. During his time at the John Innes Centre, his treatise with Peter Day, the first edition of Fungal Genetics (1963) was released. The book gathered existing knowledge of basic biology, recombination, tetrad analysis, mating systems, and extranuclear inheritance together with a single chapter on biochemical genetics, which provided a common background to a growing community of scientists. He remained at the John Innes until 1966 when he was appointed as Professor and Head of the newly established Department of Genetics at University of Leeds. In 1976, John was appointed to the Buchanan Chair of Genetics in Edinburgh and was head of the Department of Genetics until 1984.
^Fincham, J. R. S.; Pateman, J. A. (1957). "Formation of an Enzyme through Complementary Action of Mutant 'Alleles' in Separate Nuclei in a Heterocaryon". Nature179 (4562): 741. doi:10.1038/179741a0.edit
^Kinnaird, J.; Keighren, M.; Kinsey, J.; Eaton, M.; Fincham, J. (1982). "Cloning of the am (glutamate dehydrogenase) gene of Neurospora crassa through the use of a synthetic DNA probe". Gene20 (3): 387–396. doi:10.1016/0378-1119(82)90207-4. PMID6299898.edit