Born in Lumberton, North Carolina, McLean earned a bachelor’s degree in landscape architecture in 1969 from North Carolina State University, where he studied under Lewis Clarke, an early advocate for ecological design and planning. Following a stint in the U.S. Navy, McLean worked in the office of architect Arthur Gould Odell, Jr., and the Maryland Department of Forests and Parks before founding the landscape architecture firm Geoffrey McLean & Company in Raleigh, North Carolina, in 1971. McLean worked on recreational, institutional, and commercial landscapes and planning projects across North Carolina. His office took on many projects on the campus of his alma mater, including the M.E. Gardner Memorial Arboretum and the Burlington Nuclear Lab Area, the latter of which became a regionally significant example of the wider sculptural landscape movement.
His interest in stormwater and soil conservation later led him to take classes in civil engineering and become licensed as an engineer. His artfully constructed permanent sediment trap designed for Raleigh’s Eastgate Park earned an ASLA Merit Award in 1974. McLean was a member of the Wake County Planning Board, the Wake County Soil and Conservation District Board of Supervisors, and the North Carolina chapter of the American Society of Landscape Architects, serving as its president from 1979 to 1981.