In 1900 the family were living in house 3, Tamlaught, Fruithill, Londonderry. Thomas Jnr had two elder brothers, John and Samuel and an elder sister, Annie Mary.
Thomas joined Northern Bank in 1915 at Head Office.
McCunn volunteered and enlisted into the Army Service Corps (ASC) – Mechanical Transport. Later he was attached to the 59th Siege Battery, Royal Garrison Artillery. His Service Number was M/345384.
McCunn died (of pneumonia) on active service on 21st April 1918 and is buried in Wimereux Communal Cemetery, Pas de Calais, France.
He was awarded the British Victory Medal and the British War Medal.