John Morrissey studied microbiology at University College Cork, graduating with a bachelor's degree in science in 1990.
[citation needed] From 1998 to 2000 he worked and researched at the John Innes Centre (JIC) in Norwich, UK, and dealt with drug resistance of fungi to antibiotics produced by plants and with natural fungicides from bacteria.
[4] He continued this work after moving to University College Cork in 2000, where he collaborated mainly with the Irish microbiologist Fergal O'Gara to investigate the interactions of root bacteria with their host plants and their fungicidal properties.
[8] From 2010 onwards Morrissey was also working on the biotechnological use and metagenomics of marine organisms,[9] especially of sponges (Porifera),[10] to which he also wrote several book chapters.
Along with Prof Ken Wolfe of University College Dublin, he represents Ireland of the International Commission on Yeasts (ICY).