Born on July 16th 1922 in Milgaudžius village in the Tauragė region to Juozapas and Marija. He came from a farming family, the eldest child of four. Juozas was active in the local church, and at about the age of 10 decided he wanted to be a priest. He studied at Gaurės primary school, Tauragė High school and the Telšiai seminary. During the war he moved to the Kaunas seminary. He was drafted in the Red Army in 1941. He fled into Germany with his mother, sister and two brothers. They remained in DP camps, he was able to continue his studies at Eichstatte Seminary. Following the end of the war, he travelled to Rome to continue his seminary studies. He studied at the Gregorium and Angelicum University.In 1946 he joined the Marian fathers and continued his studies in America, Marina Hills Marion Seminary not far from Chicago. He was ordained on Ascension Thursday 22 May, 1952 at St Raimund Cathedral. In 1953 he moved to St Gabriel the Archangel Lithuanian parish, in Milwaukee. Juozas wanted to further his studies, which he did at Jesuit University of Marquette. In 1956 he served as parish priest at St Peters in Kenosha, where he obtained US citizenship.
He served as Chicago as provincial secretary of his order.
In 1963 he was sent to Argentina, where he learnt Spanish. He worked at Lithuanian parish of Santa Fe then in 1967 transferred to Aušros Vartos parish in Avellaneda Buenos Aires where he worked for 17 years.
When Adelaide priest, Father Spurgis became ill, Juozas came to Adelaide initially for three months. He returned to Argentina but was again summoned to help in Adelaide.From July 1984, he became the Adelaide priest. During his time here he also became the Spanish migrant chaplain having learnt Spanish in Argentina.
Father Petraitis served the Adelaide Lithuanian community until the age of 91 when he moved into a nursing home. He was able to recite the Rosary prayer in five languages, Lithuanian, Latin, German, Spanish and English. He also spoke passable Italian and Portuguese.He returned home to Lithuania just once in 1994, for a six week visit.