Born in Birkirkara on the 8th January 1909, Mamo graduated BA and LL.D. at the Royal University of Malta. He was awarded the Government traveling scholarship and the Bugeja scholarship, which enabled him to take short courses at the University of London and of Perugia. In 1936 he was appointed member of the commission and was entrusted with the task of preparing a revised edition of all the Laws of Malta. He joined the Attorney-General’s Office as Crown Counsel in 1942, was appointed Senior Crown Counsel (1950-52) and Deputy Attorney General (1955-56), and served as Chief Legal Adviser under four Prime Ministers. Mamo was professor of Criminal Law at the University of Malta. For many years he was member of the Senate and President of the University Council. In 1957 he was appointed Chief Justice and President of the Court of Appeal. In 1964 he became the first President of The Constitutional Court while in 1967 he was appointed the first President of the Court of Criminal Appeals. In 1971 he was appointed Governor General, the first and only Maltese to hold that office. On Malta becoming a Republic, Mamo was elected by the Maltese Parliament as the country’s first President. In 1960 he was nominated Knight bachelor, the last Maltese dignitary to be so honoured. He is also, as former President of Malta, a Companion of Honour of the National Order of Merit.
Mamo married Margaret Agius and they have three children.