MacDonnell was born on 7 March 1844 in Ireland. He served in various positions in Bihar and Bengal before first post in charge of a region in British South Asia as the Chief Commissioner of Burma. MacDonnell occupied the Lieutenant Governorship from 1893 to 1895. He was a member of the Viceroy's executive council during this time, and he was occupied providing famine relief. After his time as Chief Commissioner of Burma, MacDonnell was appointed Chief Commissioner of the Central Provinces.

In 1895 MacDonnell moved from Bengal to become Lieutenant Governor of the North-Western Provinces and Oudh, which would later become known as the United Provinces. His time in this position was spent providing famine relief, as he had done in the past elsewhere. This was his last post in India. He turned down a second spell as Lieutenant Governor in 1898. MacDonnell retired in 1901 due to failing health.