Juan Antonio (John) Masso (1932–2003) was the second head of Opus Dei in Australia, succeeding Fr James Albrecht who established Opus Dei in Australia in 1963. His title was Regional Vicar of Opus Dei or counsellor of Opus Dei in Australia.
Fr John showed transparency in his leadership as counsellor of Opus Dei in Australia. During the protests in the 1970s against Warrane College, Fr John approached the Sydney Morning Herald to show Opus Dei's side to the story. Eventually, calls for the closure of Warrane College were rejected by the University of New South Wales.
Fr John had many friends including non-Catholics, for example the Australian Presbyterian moderator, the Reverend Fred McKay. Whilst counsellor of Opus Dei, the movement spread from Sydney to Melbourne, Auckland, Hamilton Tasmania with activities in Perth, Brisbane, Canberra, Newcastle, Wollongong and many other places. Fr John was made monsignor by the Archdiocese of Sydney.
Fr John died in Pamplona Spain, after passing by Argentina where he had a conference with the Prelate of Opus Dei, Bishop Javier Echevarria. Upon his death, a requiem Mass was celebrated in St Marys Cathedral by Cardinal George Pell included his predecessor as Archbishop of Sydney, Cardinal Edward Clancy, the Bishop of Lismore, Bishop Geoffrey Jarrett, the Bishop of Broken Bay, Bishop David Walker, Bishop David Cremin and Mons Masso's newly appointed successor, Fr George Rossman. The preacher at the Mass said that Fr John had no enemies. Cardinal Pell remarked, "That's not the Opus Dei I know".
In an interview with the Sydney Morning Herald, Fr. John was asked why, when such a command was basic to many Christian denominations and groupings, a special organisation was needed to promote the sanctity of everyday work. Fr John replied, "Yes, you are right. But how many people do it?".
Fr John's collaborators and friends have set up The Masso Foundation, to continue the work he tirelessly carried out during his life.