Professor Cassidy was awarded a diploma in Applied Science by Dublin Institute of Technology, his BSc (Applied Sciences) by University of Dublin, and completed his PhD at the University of Utah. He has since lectured in Analytical Chemistry in DIT, Kevin Street. He was appointed Assistant Head of School in 2001 and awarded Professorship of DIT in 2009.
His research interests include Analytical Chemistry and Instrumentation. This involves the theory and operation associated with Modern Analytical Instruments in the area of spectroscopy, electrochemistry and chromatography.