Born in Valletta in 1918, Micallef studied at the Lyceum and the Royal University of Malta from where he graduated B.Sc. in 1939.
In common with many university students in that year, which marked the start of World War II, he was commissioned into the RMA in the rank of 2nd lieutenant. A year later, he was promoted captain when serving in a heavy anti-aircraft battery in Egypt.
Having returned to Malta in 1942, he served as battery commander with the 2nd Heavy Anti-Aircraft Regiment RMA in the rank of major. Later he sewed as adjutant in the 1st Coast Regiment of the RMA. In 1949 Micallef attended the Military Staff College at Camberley where he graduated as PSC (Graduate of Staff College).
Micallef also served as battery commander with various regiments in Malta and carried out staff duties in the UK, Egypt, and Belgium. In 1961 he was appointed second-in-command of the 2nd Light Anti-Aircraft Regiment RMA in Malta. Two years later he was posted to Germany where he assumed command of the 1st Regiment RMA in the rank of lieutenant-colonel.
In 1966 Micallef returned to Malta to assume command of the RMA which had one regiment still posted in Germany and another in Malta. He was appointed colonel and also assumed command of the Malta Land Force a year later. This was the delicate period when the British government had decided to disband the RMA, but the Maltese government decided to retain all personnel in the Malta Land Force.
In 1969 Micallef retired from the British Army but continued to serve as commander of the Malta Land Force in the rank of brigadier, formally retiring in 1972. Micallef was decorated by Her Majesty’s Government as member of the Order of the British Empire (1966) and as Commander of the Order of the British Empire (1969). In 1992 he was appointed member of the National Order of Merit (MOM).
In 1944 Micallef married Yvonne Maxwell and they have three children, Peter, Jacqueline, and Suzanne.