On 4th August 1914 the UK decared war on Germany. Four days later Harvey joined the 5th Battalion, Gloucestershire Regiment with the rank of private. Three months later he became a Roman Catholic. His battalion was posted to France in March 1915 where he was promoted to Lance Corporal. He was also awarded the Distinguished Conduct Medal. While on patrol he and another solder encountered the enemy. Between them they killed three Germans and captured their rifles and a pistol. Harvey returned to England for officer training and received his commission. He returned to the front-line in France but, in August 1916, was captured, spending the rest of the war in German prisoner-of-war camps.

Harvey was already a prisoner-of-war when his first volume of poems were published. It was called "A Gloucestershire Lad At Home and Abroad." Remarkably he was permitted to send his poems back to England and in 1817 "Gloucestershire Friends" was published. His third volume of poems was entitled "Ducks, and other Verses". The collection was named after a poem of the same name, which was most probably his most popular poem.

F.W. Harvey returned home to England in 1919. In 1921 he married Sarah Anne Kane, an Irish nurse. They had two children and lived a modest life. He continued to practice law with offices in Lydney, but often waived his fees. He continued to right and began a relationship with BBC Radio Bristol in 1928, which including writing and occasionally broadcasting radio programs.

Harvey served with the Home Guard during World War two, but his health began to deteriorate thereafter. The BBC dedicated a whole program to him in 1956 called "Sing a Song of Gloucestershire". He died at Yorkley in February 1957.