Known as William, he was the son of William Seymour and Lydin Seymour of 56 Glen Road, Andersonstown, Belfast. The family were of Church of Ireland faith.
In 1911 the family are living in house 15, Stranmillis Park, Belfast.
Following his education at RBAI (Inst), Belfast, in March 1913, Seymour joined Northern Bank at Head Office. Transfers to Donegall Square (1913) and Head Office (1914) followed.
Whilst working for the bank, he was also a member of the Queen's University Officer Training Corps from 1st November 1915 to 21st January 1916.
He volunteered and enlisted into the 10th Bn. Royal Irish Fusiliers as a Private. On 19th December 1916, he was promoted to 2nd Lieutenant and posted to the 9th Bn. Royal Irish Fusiliers as part of the British Expeditionary Force.
Seymour fought in the battle at Ypres (1917) before being Killed in Action on 16th August 1917 with the 10th Bn. Royal Irish Fusiliers. This was the date of the Battle of Langemarck (3rd Ypres).
Private Brady of the battalion reported:
"He was in command of VIII platoon. He was a young man and I knew him well; he was fair and very nice and well liked by everyone. I saw him during the attack; we were well over the ridge to the left of St Julien. I was only 10 yards off him when I saw him killed outright by a piece of shrapnel. I was wounded very shortly afterwards. I have heard since that we took our objective that morning but got driven back again, so perhaps the Germans would get his body."
Seymour was awarded the British Victory Medal and the British War Medal and he is commemorated on the Tyne Cot Memorial, Flanders, Belgium.
The Belfast News Letter of 6th January 1919 reported: