Among other things, he chairs the Executive Committees of the Pan African Citizens’ Network (PACIN), formerly known as the Centre for Citizens' Participation in the African Union (CCP AU) and the International Coalition for the Responsibility to Protect. He is a former Chair of the African Court Coalition and is also a Councillor (and former Secretary) of the African Forum of the International Bar Association. He is also a former member of the Executive Committee of the International Institute of Law Association Chief Executives .

Mr. Deya is an Advocate of the High Court of Kenya, and was previously the CEO of the East Africa Law Society (EALS), and, before that, Deputy CEO of the Law Society of Kenya. He has also worked with the Kenyan Section of the International Commission of Jurists. While at the EALS, he founded the East African Civil Society Organizations’ Forum.