In 1805, Fr. Deshayes was appointed parish priest of St. Gildas, Auray. He was a good preacher. He started a school for boys, another one for girls, a college and a minor seminary. He started a co-operative bank to give loans to the poor, a spinning mill and a hospice. In 1816, he was the Vicar General of the Diocese of Vannes. In 1816, Fr. Deshayes started a novitiate to form Brothers to teach in rural schools and in 1819, he got this new Institute of Brothers amalgamated with a similar one started by Fr. Le Mennais. This was the beginning of the Ploermel Brothers. In 1807, he founded Sisters of St.Gildas.
On 17th December, 1820, Fr. Deshayes was officially admitted into the Company of Mary and on the same day he was elected Vicar General of the Montfortian congregations. He recruited many young men and started a novitiate for Brothers. In 1823, he wrote a Directory for the Brothers. As legal approval for teaching in schools was obligatory, he got an official recognition from the government as the Institute of the Brothers of the Holy Spirit and Brothers were allowed to teach in five Provinces. On 22nd September 1824, 42 Brothers made their annual vows. In 1825, Fr. Deshayes went to Rome to get the Rules of the Company of Mary and Daughters of Wisdom approved by Rome and to work for the beautification of Montfort. On 7th September 1830, Montfort was declared Venerable. In 1835, there were brothers, novices and postulants put together 132, of whom 57 continued to stay in the Holy Spirit House while 75 were attached to St. Gabriel’s House i.e., 33 of them had their residence there and 42 were teaching in various schools. “The Brothers chose from their own number a Superior who was to govern the Congregation”. He signed the Rule on January 7 ,1837 and it was approved on April 9, 1838 by the Bishop of Lucan. This Rule was to be kept as a secret and it was to come into effect only after Fr. Deshayes’ death. Fr. Deshayes altogether started 76 schools and out of those 29 were given up during his lifetime itself. ln 1838, he founded St. Gabriel’s Boarding School in St. Laurent. One of his greatest achievements is the founding of schools for the deaf and schools for the blind. Thus La Chartreuse, Rouille, Orleans and Lilly were centres started by him for the handicapped children. After a full life of missionary activities and after contributing much to the Montfortian Congregations, Fr. Deshayes died on 28 Dec, 1841. He was buried in the Daughters of Wisdom cemetery, actually at the 14th Station of the Way of the Cross that he had erected. After the death of St. Louis Grignion de Montfort in 1716, it is Fr. Gabriel Deshayes who gave a new life and re-founded the society of Montfort Brothers of St. Gabriel. He is considered as the second founder of the society. Before his death, he declared, “Even if I had only one more week to live, I would still plan for some more good works to be done”.