After studying for her undergraduate degree at the University of Kent, Lennon obtained her master's degree and doctorate from the University of Oxford. In 1979, she was employed as a lecturer by the University of Hull. Lennon was one of the founders of the university's Centre for Gender Studies in 1986, and of the Society for Women in Philosophy in 1989.
After thirty years at the university, Lennon was appointed Ferens Professor of Philosophy. On 2 March 2009, she gave her inaugural lecture, entitled 'Re- enchanting the World: the role of Imagination in Perception', at the Middleton Hall lecture theatre.
- Explaining Human Action (London: Duckworth, 1990).
- Philosophy of Mind, with Steve Burwood and Paul Gilbert (London: Taylor and Francis, 1998).
- Theorizing Gender, with Rachel Alsop and Annette FitzSimons (Cambridge: Polity, 2002).
- The World, the Flesh and the Subject: Continental Themes in Philosophy of Mind and body, with Paul Gilbert (Edinburgh: Edinburgh University Press, 2005).