Mary Forrest was educated at the National Botanic Gardens, University College Dublin and Trinity College Dublin. Following graduation from UCD she was appointed Heritage Gardens Fellow by An Taisce, to prepare an inventory of trees and shrubs in exotic plant collections in Ireland. This work was subsequently published asTrees and Shrubs cultivated in Ireland. She then became Head gardener at Glenveagh National Park, Co. Donegal. She was appointed lecturer in UCD in 1986 where she has since taught courses in Landscape Management, landscape trees and shrubs, garden history and Fundamentals of Horticulture to students taking degrees in Horticulture and Landscape Architecture.
Her research interests include history of designed landscapes in Ireland, cut foliage production, urban forestry and e-learning in horticultural education.
She has been involved in European funded projects namely, Concerted Action ( examining minor specialist crops)
Cost Action (Urban forests and trees) and Erasmus Mundus ( Fourth level agricultural education in Europe).