After ordination he was appointed to Corpus Christi, Gateshead, where he remained until January 1935. From January 1935 until January 1943 he was assistant priest at St. Fdward's, Whittey Bay. He was then appointed to St. Cuibbert's, Hartlepool, where he remained until his appointment in 1947 to St. Joseph's, Langley Moor. He remained here until 1949. In that same year he was appointed by Bishop McCormack as first parish priest of Immaculate Heart, Sunderland, a new parish to serve the people of Springwell, Humbledon and Plains Farms Districts. At first without church, house or school, Father Hannon quickly Set about his task and within 5 years of his appointment the church of Immaculate Heart had been blessed and opened, a new presbytery built and St. Cuthbert's School opened to be shared wIth the neighbouring parish.
As its only priest, Father Hannon was to serve the area for 41 years until failing health forced him to retire to Hexham in February 1991, but it was with the people of the parish of Immaculate heart that the Lancashire born Father Hannon celebrated 60 years of priesthood in the service of the Diocese of Hexham and Newcastle.
After a short but happy stay at Carnlyne Residential Care Home, Hexham, were he was nursed with great love and devotion, Father Hannon died peacefully at the Home on Sunday, 10th May, 1992, at the age of 88 in his 61st year of his priesthood.
The concelebrated Funeral Mass took place at the Church of the Immaculate Heart of Mary, Sunderland, on Friday, 15th May and his body was laid to rest in Monkwearmouth Cemetery.
May he rest in peace.