MB BS Lond 1950, MD 1952; MRCS LRCP 1950, FRCP 1971.
Leonard held resident appointments at Westminster Hospital, Christchurch Hospital Hampshire, Ipswich and East Suffolk Hospital, National Heart Hospital, the National Hospital for Nervous Diseases and from 1958 to 1963 was senior medical registrar at MRI. In 1963, Leonard was appointed consultant physician to Withington Hospital Manchester. He was also subdean of clinical studies and lecturer in medicine at the University of Manchester. Leonard retired sometime between 1980 and 1993. He was secretary of the section of medicine of MMS.