In 1955 Hallam was appointed to the staff of the Department of Chemistry at University College of Swansea becoming Senior Lecturer in 1964 and Reader in 1970.  In 1963, Hallam took a year's sabbatical and became an adviser in physical chemistry at the new University of Nigeria at Nsukka. He had active international collaborations and was presented with a medal by the University of Helsinki in 1973 for his outstanding service and was also a visiting professor at the University of Marburg in 1975.  Hallam was known for his work in infrared spectroscopy of the hydrogen bond and as one of the founders of matrix isolation spectroscopy. He passed away unexpectedly on 14 May 1977.