Javier Cotelo was born in Madrid on 16 August 1932. While preparing to study architecture, he met several students and professors from Opus Dei. In February 1952, he applied for admission as a numerary.

In 1953, at the age of 21, he met St. Josemaría in Rome. He moved to the Eternal City in 1962, and he would spend the rest of his life. There he worked as an architect on the construction of Villa Tevere and Cavabianca, and served as St Josemaría's driver on the many apostolic trips the founder made throughout Italy and several other European countries. He went on to serve in this same role for many years, first with Blessed Álvaro del Portillo and later with Bishop Javier Echevarría.

He was also a gifted draughtsman and painter. Every Christmas at the Casa del Vicolo, his centre, he would draw a small caricature of each person to decorate the living room, and he did the same for certain special birthdays. Over the years he also painted landscapes that today adorn the walls of many homes and centres of the Work. In 1980, at the request of St. John Paul II, he took charge of the project to place an image of Our Lady in St. Peter's Square: the Mater Ecclesiae mosaic that still stands today to the right of the basilica's façade.

Javier lived as a son who knew he was loved, and as an elder brother who felt responsible for passing on to others everything he had received from God in daily life, in little things, and with great affection.