Son of Evan and Mary Evans, of Trawsfynydd, Merioneth. One of the war poets, who wrote poetry under the name 'Hedd Wyn'.

Ellis was born on 13 January 1887, and was the first of 14 children. He began writing poems at the age of 11. He mastered the hardest form of Welsh poetry (the cynghanedd) at the age of 12, and continued to write after leaving school to work on the farm at the age of 14. By 19, he was a regular competitor. He took the first of the six poetry chairs he would win in competition in 1907 and was awarded his bardic name Hedd Wyn ('white peace') in 1910.

Ellis had no intention of fighting, but was conscripted into the Royal Welsh Fusiliers in February 1917. He was allowed home for a few weeks that spring to help with the farm, but was in France by June 1917. On 31 July 1917, the first day of the Third Battle of Ypres, he was hit by a piece of trench mortar shell near Langemark and died at a nearby aid post.

Soon after his departure on active service, he completed the poem Yr Arwr (The Hero), his entry for the 1917 National Elsteddfod, for which he was posthumously awarded the poetry chair.

His style, which was influenced by romantic poetry, was dominated by themes of nature and religion. He also wrote several war poems following the outbreak of war on the Western Front.