Born on 15 August 1946 in Ikwerre Local Government Area, Rivers State, Nigeria, Achinewhu had his primary education in his home town Aluu. He finished from County Grammar School, Ikwerre/Etche in 1963 with Grade One. He later proceeded to  Government Secondary School, Owerri and got his Higher School Certificate in physics, chemistry, and zoology in 1965. In 1970, Achinewhu graduated from the University of Ibadan, B.Sc. second class honors, M.Sc. in 1972 and Ph.D. 1975 in food science and technology from University of Reading, UK.