Thomas Baker Brown was born on the 22nd December 1896 at 158 Linskill Street in Tynemouth. He was the son of Thomas Baker Brown, an insurance agent, and J. H. Brown. He was the middle child of three siblings including his elder brother George and his younger sister Hazel. Later the family moved to 36 Drummond Terrace in North Shields, where Brown attended Kettlewell School, and then went on to work as a clerk.

On the cusp of his 19th birthday, Brown joined the H.M. Army at the Scottish Presbyterian Church Hall in Howard Street, North Shields on Friday 26th November 1915. By the 5th December 1915, Brown had travelled to a training camp at Scarcroft Schools in York serving in the 'Clerks Platoon' for the 6th Northumberland Fusiliers. At the camp, Brown received training in bombing, signalling and musketry, though he suffered from poor eyesight and was issued with glasses. After failing to be transferred to the Royal Flying Corps, Brown was placed into the signalling section around the 9th March 1916. Some months later, on 18 July 1916, Brown was drafted to France alongside his brother George, as part of the 2/6th Northumberland Fusiliers, 32nd Division.

By the 1st August 1916, Brown was moved to the 21st Northumberland Fusiliers (2nd Tyneside Scottish 37th Division) and was sent on his first journey to the front line trenches. Later, in March 1917 Brown was awarded the Military Medal for his 'heroism' and 'bravery'. Brown visited the front line tranches many times over the following months, and remained uninjured, but on 21st March 1918 he was taken prisoner by German soldiers on the Arrasfront at Bullecourt. He was taken to Germany where he was placed into a prisoner of war camp in Dülmen and then transferred to Limburg by April 1918. Here, Brown worked at the Pit North Star, a coal mine in Herzogenrath. On the 17th November 1918, on witnessing the command of the German camp breakdown, Brown and a party of five other men walked out of the gates. They made their way to Holland, arriving at Amersfoot then travelling on to Rotterdam on 3rd December. From here, Brown boarded the S.S. Arbroath and arrived in Hull on the 8th December. Finally he was able to take a train to a reception camp in Ripon, the last stop before his journey home.

Years later, in the 1930s, Brown suffered from an eye disease which left him blinded for five years. Specialists attributed it to his time spent in the prisoner of war camp, and in particular having to work in the mines in poor conditions. Brown only ever partially recovered his sight. As a result, he was rejected several times to fight in World War II, and served on the Home Front instead.