Dennis is the Professor of Education at the University of Derby and the Director of the influential campaign group Academics For Academic Freedom (AFAF), which he founded in 2006. He was a columnist for the 'Times Educational Supplement' and is a member of the editorial board of the 'Times Higher Education' magazine. In 2009 he edited and contributed to a special edition of the 'British Journal of Educational Studies' on Academic Freedom and he writes regularly in the national and international press on free speech and academic freedom. His latest book due out in 2014 is entitled 'The "Limits" of Academic Freedom'.

Dennis is in constant demand around the world as speaker on academic freedom and in 2010 he took part in the 50th Doha Debate alongside Professor Tariq Ramadan, defending the proposition ‘Education is worthless without freedom of speech’ a programme with a potential audience of 350 million people. In the educational world he is well-known for his controversial co-authored book 'The Dangerous Rise of Therapeutic Education' (2008) which has been described as ‘one of the most important books to have been written in at least the last twenty years in that crucial area where philosophy, policy and practice coincide’.

In 2011 he was appointed by Boris Johnson as a member of the Mayoral Education Inquiry, a team formed to improve the standards of education of London’s children and young people.

Dennis is also the Honorary Secretary of the Standing Committee for the Education and Training of Teachers (SCETT) a charity formed in 1981 by the major teaching unions and professional associations to advance the interests of teachers in teacher education and training.