Leonard Pfeil was first appointed a Junior Lecturer in Metallurgy in the newly formed Metallurgy Department of the University College of Swansea, where he worked on the metallographic problems of steel and was awarded a D.Sc by the University of London in 1927.
In 1930 he moved to Birmingham to work at the Mond Nickel Company as Assistant Manager of their Research and Development Department.
Manufacturing techniques for the successful Nimonic range of nickel alloys were significantly improved.
Other projects included the development of diffusion membranes for the separation of uranium isotopes.
In 1960 he became Vice-Chairman of International Nickel Limited, the United Kingdom branch of the parent firm, holding the post until his retirement in 1963.