Ganwyd Gweneth Lilly ar 24 Medi, 1920 yn Lerpwl ac yn y fan honno y cafodd ei magu. Yr oedd yn unig blentyn i rieni â'u gwreiddiau ym Môn. Cafodd ei haddysg yng Ngholeg Merched Lerpwl ac, yna, astudiodd Saesneg ym Mhrifysgol Lerpwl a chael ei phenodi wedyn yn ddralithydd llenyddiaeth Saesneg yno. Symudodd gyda'i mam i Gymru yn 1946 i ddysgu Saesneg yn hen Goleg y Santes Fair ym Mangor ac yno y bu hyd ei hymddeoliad ym 1977. Ymgartrefodd yn Llanfairfechan. Bu farw ar 5 Ebrill, 2004.
Enillodd Gweneth Lilly Wobr Tir na n-Og ddwywaith yn olynol gyda'i nofelau hanes Y Drudwy Dewr, seiliedig ar chwedl Branwen, a Gaeaf y Cerrig, 1981 a 1982. Bu'n hynod gynhyrchiol rhwng dechrau'r 80au a chanol y 90au gan ganolbwyntio'n bennaf ar y nofel hanesyddol. Enillodd ei phlwy yn fuan fel un o'n hawduron mwyaf blaenllaw ar gyfer plant a phobl ifanc. Yn 1982, blwyddyn saith canmlwyddiant marwolaeth Llywelyn ap Gruffydd, Llywelyn ein Llyw Olaf, fe'i comisiynwyd i ysgrifennu nofel i nodi'r digwyddiad - Rwy'n Cofio dy Dad.Ysgrifennodd ddwy nofel Saesneg Treason at Trefriw ac On a Scaffold High ym 1990 a 1993. Fodd bynnag, ar y nofel Gymraeg y canolbwyntiodd yn bennaf gan gyhoeddi 13 o lyfrau i gyd, gan gynnwys ei hunig nofel i oedolion, Orpheus a'i chefndir yng nghyfnod y Rhufeiniaid yng Nghymru. Cyhoeddodd ddau gasgliad o straeon byrion, Masgiau a Dynes Mewn Du.
Yn aelod brwd a gweithgar o gymdeithas hanes ardal Llanfairfechan, ysgrifennodd hefyd nifer o gyfrolau Cymraeg a Saesneg o ddiddordeb lleol a golygu rhai eraill.
Gweneth Lilly was born on 24 September, 1920 in Liverpool and was brought up in the city. She was an only child to parents with their roots in Anglesey. She was educated at Liverpool Girls' College and then read English at Liverpool University before being appointed lecturer of English literature there. She moved with her mother to Wales in 1946 to teach English at the old St Mary's College, Bangor and she remained there until her retirement in 1977. She lived in Llanfairfechan and died on 5 April, 2004.
Gweneth Lilly was awarded the Tir na n-Og prize twice over consecutive years with her historical novels Y Drudwy Dewr, based on the legend of Branwen, and Gaeaf y Cerrig, 1981 and 1982. She was particularly productive during the mid-80s and 90s, concentrating mainly on the historical novel. She became renowned as one of our most prominent authors for children and young people. In 1982, to commemorate the seventh hundred anniversary of the death of Llywelyn ap Gruffydd, Llywelyn the Last Prince of Wales, she was commissioned to write a novel to note the event - Rwy'n Cofio dy Dad. She wrote two English novels Treason at Trefriw and On a Scaffold High in 1990 and 1993. However, she concentrated on the Welsh novel and published 13 books in all, including her only novel for adults, Orpheus based on the Roman period in Wales. She, also, published two collections of short stories, Masgiau and Dynes Mewn Du.
She was an enthusiastic and diligent member of Llanfairfechan's historical society and wrote and edited extensively in Welsh and English on matters of interest.
