James Harrison Renwick was born in Otley, Yorkshire on 4 February 1926. He was educated at Sedburgh School winning a Harkness Scholarship to the University of St Andrews in 1943. He studied medicine, graduating MB, ChB in 1948. After various hospital appointments, 1948 to 1951, Renwick did his national service in the Royal Army Medical Corps 1951-1953, serving in Korea and seconded part-time to the Atomic Bomb Casualty Commission, Japan (final rank of Captain). In 1953 Renwick was awarded a Medical Research Council grant to train in Human Genetics. He undertook this work in the Galton Laboratory of University College London, studying under Lionel Sharples Penrose and John Burdon Sanderson Haldane (PhD 1956).
Renwick spent a period 1958-1959 working under Professor Victor Almon McKusick at the Johns Hopkins Hospital Department of Human Genetics (appointment as Physician). On his return to the UK in 1959 he took up a post as Research Fellow in Guido Pontecorvo's Department of Genetics at Glasgow University. He was appointed Senior Lecturer in 1960, Reader in 1966 and Titular Professor in 1967. In 1968 Renwick moved to the London School of Hygiene and Tropical Medicine as Reader in Human Genetics in the Department of Community Health and Head of the Preventive Teratology Unit. In 1978 he was appointed Professor of Human Genetics and Teratology, and also became Honorary Consultant Counsellor in Human Genetics at St George's Hospital, London. He retired in 1991.
Renwick made a fundamental contribution to modern genetics, in particular to the development of human gene mapping that paved the way for the Human Genome Project. Working initially at the Galton Laboratory, University College London, with Lionel Sharples Penrose, then at the University of Glasgow, and latterly at the London School of Hygiene and Tropical Medicine, for a period of nearly 20 years up to the early 1970s, he pioneered the use of genetic markers to map disease genes on human chromosomes, seeing this field develop from its infancy at a time when there was virtually no information on mapping human genes to a major international scientific endeavour. His Independent obituarist notes that, "His work linking the ABO blood groups and the nail-patella syndrome was seminal and is still cited as a classic in human linkage analysis" and he was behind the first generalised computer program for calculating LODs (Logarithm of Odds) for large human pedigrees. He also was involved in a major ongoing transatlantic collaboration on gene mapping with Victor Almon McKusick, making many visits to Johns Hopkins as a consultant on the application of computer techniques to genetical linkage, building on mathematical work initiated by Cedric Austen Bardell Smith at the Galton Laboratory. Renwick's key role in this work was due to his expertise in three essential areas: the clinical assessment of the families with specific genetic disorders, the laboratory analysis of the genetic markers and the mathematical and computing approaches to the data obtained.
In 1972 he radically changed direction, following what he described as a "unilateral termination of computer facilities" at Johns Hopkins and his consequent "ejection from the field". The subsequent years of his career at the London School of Hygiene and Tropical Medicine were mainly spent on analysis of causative factors in human malformations, studying in particular birth defects with an early study on the possible relation between toxins in potatoes and anencephaly and spina bifida (ASB).
Renwick was active in a number of genetical societies, including the Genetical (later Genetics) Society, which he served as Honorary Treasurer 1960-1965 and then auditor 1965-1972. He was a founder of the Developmental Pathology Society, serving as its President. He was also active in social activities at the London School of Hygiene and Tropical Medicine. Renwick was made a Fellow of the Royal College of Physicians of Glasgow (1970) and the Royal College of Physicians of London (1974) and a Fellow of the Royal College of Pathologists (1982). He was awarded the University of London DSc in 1970. He died on 29 September 1994.