[1] Macdonnell was educated at Trinity College, Dublin[2] and was placed in the first class in the final divinity examination in 1846.
[3] He was ordained deacon in 1846 and priest in 1847, and began his career as a Curate at St. Patrick's Cathedral, Dublin.
That year, he was asked by his college friend William Connor Magee (at this point Bishop of Peterborough) to become Vicar of St Mary's Leicester,[5] moving two years later in 1875 to Rector of Walgrave,[6] and in 1880 to Rector of Misterton, Leicestershire;[7] He was private chaplain to Bishop Magee throughout his time as bishop of Peterborough (1873–1891), and in 1878 was appointed an Honorary Canon of Peterborough Cathedral,[8] changing in 1883 to a Residentiary Canon at Peterborough.
[9] He wrote several books including a biography of his old friend, Life and Correspondence of William Magee (1896),[10] described at the time as one of the more outspoken pieces of ecclesiastical biography printed.
His wife had died seven years earlier, and he was survived by a son, Frederick T. Macdonnell, and a daughter Charlotte Jane Macdonnell, who married Sir Shirley Salt, 3rd Baronet.