Famous for his aphorism 'Work expands so as to fill the time available for its completion' he was British naval historian and author of some sixty books - the most famous of which was his bestseller Parkinson's Law - which led him to be also considered as an important scholar within the field of public administration.

He attended St. Peter's School in York before gaining a place at the University of Cambridge and receiving his BA degree in 1932. In 1934 he enrolled as a graduate student at King's College London. He was commissioned into the Territorial Army as a member of the 22nd London Regiment (The Queen's) and was promoted to Lieutenant. Emmanuel College, Cambridge elected him a research fellow. In 1935 he wrote his Ph.D. thesis on Trade and War in the Eastern Seas, 1803-1810, which was awarded the Julian Corbett Prize in Naval History. He took up the position of senior history master at Blundell's School in Tiverton, Devon in 1938

In 1943 he bought Elham manor before being appointed lecturer in history at the University of Liverpool from 1946 to 1949.

1950 saw him appointed Raffles Professor of History at the newly-established University of Malaya in Singapore. While there, he initiated an important series of historical monographs on the history of Malaya, publishing the very first of the series in 1960. A movement developed in the mid-1950s to establish two campuses, one in Kuala Lumpur and one in Singapore. Parkinson actively attempted to persuade the authorities to avoid dividing the university, but to maintain it to serve both Singapore and Malaya in Johor Bahru. His efforts were unsuccessful and the two campuses were established in 1959. The original Singapore campus, where Parkinson taught, later became the University of Singapore.

In 1955 he published his most famous work Parkinson's Law, a book that expanded upon a humorous article that he had first published in the Economist magazine in November 1955, satirizing government bureaucracies. The 100-page book, first published in the United States and then in Britain, was illustrated by Osbert Lancaster and became an instant best seller. This collection of short studies explained the inevitability of bureaucratic expansion, arguing that 'work expands to fill the time available for its completion'. Typical of his satire and cynical humour, the book included a discourse on Parkinson's Law of Triviality (debates about expenses for a nuclear plant, a bicycle shed, and refreshments), a note on why driving on the left side of the road (see road transport) is natural, and suggested that the Royal Navy would eventually have more admirals than ships. After serving as visiting professor at Harvard University in 1958, and the University of Illinois and the University of California, Berkeley in 1959–60, he resigned his post in Singapore at the University of Malaya to become an independent writer and celebrity. To avoid high taxation in Britain, he moved to the Channel Islands and settled at St Martin's, Guernsey, where he purchased Les Caches Hall and later restored Annesville Manor. His writings from this period included a series of historical novels, featuring a fictional naval officer from Guernsey, Richard Delancey, during the Napoleonic era .

He moved to the Isle of Man in 1985 and then to Canterbury in 1987. He died in March1993, at the age of 83. He was buried in Canterbury. Blue Plaque at 36 Harkness Drive, Canterbury