Critien was born in Sliema in 1949 and graduated BA (Gen) in 1972 from the RUM, and continued his studies at the University for foreigners of Perugia. He setteled in Pisa for 22 years where he taught English Language and Literature at the Scuola Mondolingue.
John Critien joined the Sovereign Military Order of
St John of Jerusalem to do voluntary work and became a lay member in 1983. In 1989 he joined the religious Order, spending three months as aspirante followed by a one-year novitiate.
In June 1990 Critien took vows of poverty, chastity, and obedience before Fra Andrew Bertie, grand master of the Order, the first step towards becoming a fully- professed knight. The ceremony took place at the seat of the Order in Via Condotti, Rome in the presence of two witnesses.
In May 1993 Critien made his solemn profession in Pisa. He was elected member of Sovereign Council (Government) of the Order in 1994 and held this position until 1999. Between 1994 and 2004 he lived at the world headquarters of the Sovereign Order in Palazzo Malta. During these years John Critien was conservator of the Magistral Palace Library and Archives and Curator of the art collections of the Order.
In July 2000 Critien was appointed Knight resident at Fort St Angelo, a position he currently holds. In 2001 he was elevated to the rank of Knight Grand Cross of Justice, the first ever Maltese to hold this grade in the Order. He has been received into various orders of chivalry and honoured with the award of various prestigious decorations.
John Critien has published articles of historic and artistic nature on subjects such as bookbindings, numismatics and rare manuscripts in the Magistral Palace Archives in Rome.