After finishing primary school, Mirko went to Zagreb and attended the Technical Chemistry High School. He enrolled in chemistry at the Faculty of Sciences, University of Zagreb in 1961. After graduating Chemical Engineering (1966) he began his scientific career at the Ruder Boskovic Institute as an assistant in the Laboratory of Nuclear Chemistry, Department of Physical Chemistry.
He enrolled in postgraduate studies at the Faculty of Sciences in Zagreb and completed his M.Sc. thesis in 1968. The title of his M.Sc. thesis was “The Nuclear and Chemical Study of (n, gamma) Reactions”. Two years later (1970) he obtained his Ph.D. with a thesis, entitled “The Study of (n,He-3) and (n,t) Reactions on Middle Weight Nuclei”. Dr. Diksic completed his postdoctoral studies at the McGill University Department of Chemistry in Montreal, Canada, (1971-1973), where he studied proton induced nuclear reactions and the development of fast chemical separations. He was appointed as a Research Associate in 1974 at the McGill University Department of Chemistry and in 1978 he joined a group of scientists who were starting a PET (Positron Emission Tomography) program at the Montreal Neurological Institute.