After his PhD, Green undertook a postdoctoral research year with Wilkinson before moving to the University of Cambridge in 1960 as Assistant Lecturer and being appointed a Fellow of Corpus Christi College, Cambridge in 1961. In 1963 he was appointed a Septcentenary Fellow of Inorganic Chemistry at Balliol College, Oxford and a Departmental Demonstrator at the University of Oxford. In 1965 he was made a Lecturer and he was also a Royal Society Senior Research Fellow in Oxford 1979–86. In 1989 he was appointed Professor of Inorganic Chemistry and Head of the Inorganic Chemistry Laboratory at Oxford and Fellow of St Catherine's College, Oxford. In 2004 he became an Emeritus Research Professor. He was a co-founder of the Oxford Catalysts Group plc in 2006.
Green held many visiting positions including: Visiting Professor, Ecole de Chimie and Institute des Substances Naturelles, Paris (1972), Alfred P. Sloan Visiting Professor, Harvard University (1975), Sherman Fairchild Visiting Scholar at the California Institute of Technology (1981), and Walter Hieber Gastprofessor, University of Munich, Germany (1991).