Although he intended to work for a doctorate under the cytologist C. D. Darlington he was inspired to move to Sidney Sussex College, Cambridge, under the supervision of E. J. H. Corner, leading to a PhD in 1973 and D.Phil.

[1] In 1973 Mabberley was elected the first Claridge Druce junior research fellow at St John's College, Oxford, before being appointed in 1976 to a tutorial fellowship at Wadham College, Oxford (linked to a university lecturership in the Department of Botany, later Plant Sciences, where he set up the "Mablab" with graduate students and post-doctoral research workers from around the world).

In 2004 he was appointed to the Orin and Althea Soest Chair in Horticultural Science at the University of Washington, Seattle, US, where he was also Professor of Economic Botany in the College of Forest Resources.

In March 2008 he took up the newly created position of Keeper of the Herbarium, Library, Art and Archives at the Royal Botanic Gardens, Kew.

[6] Mabberley is known as a world traveller, having performed fieldwork in many countries over several decades: Kenya (1969, 1970–71), Uganda (1970–71), Tanzania (1971–72), Madagascar (1971), Malaysia, Singapore & Indonesia (1974, 1981), Papua New Guinea (1974, 1989), Seychelles (1978), Panamá (1978–79), Portugal (1984–96), New Caledonia (1984), New Zealand (1990), Sri Lanka (1991), Hawai’i (1998), Cape York, Australia (Royal Geographical Society of Queensland expedition, 2002), Malaysia (2003, 2007), Vietnam (2005), China (2006, 2008), India (2019), Japan (2019).

His archive, especially that relating to Mabberley’s plant-book is housed at the National Botanic Garden of Wales, of which he was a Trustee 2008-2011 and is an Honorary Fellow since November 2018.

In 2016 he was appointed a Member of the Order of Australia for significant service to horticultural science, particularly to plant taxonomy and tropical botany, as an academic, researcher and author.