During the First World War Felix served in the British Army as a Staff Sergeant.
Felix is most famous for writing the music for the WW1 marching song "Pack Up Your Troubles in Your Old Kit Bag and Smile, Smile, Smile” in 1915. The lyrics to the song were written by his brother George Henry Powell (1880 – 1951) - under the pen name George Asaf.
The song was entered into a competition for "best morale-building song". It won first prize and was noted as "perhaps the most optimistic song ever written".
