Kaminis was born on July 15, 1954 in New York, USA. He studied Law at the University of Athens, graduating in April 1980. His graduate studies were in France, at the Université de Paris II, where he obtained a Diplôme d ´études approfondies (DEA) degree. He received his doctorate (Doctorat d´ Etat en Droit) at the Université de Paris I.
Returning to Greece, he worked at the Law School of the University of Athens, in various capacities (lecturer, assistant professor, etc.)
Kaminis served as assistant citizens' advocate (ombudsman) from 1998 until May 2003 when he was elected ombudsman. In December 2008, he was elected to the Board of the Association of Mediterranean Ombudsmen and, in June of 2009 he was elected Vice President of the International Ombudsman Institute.
He was re-elected in 2014.
Kaminis is married and has two daughters.