Ysgol Gyfun Gymraeg Glantaf was founded in 1978, initially sharing premises with the English-language Glantaf High School, before expanding to occupy the entire building. Its first headmaster was J E Malcolm Thomas, who was succeeded upon his retirement in 1995 by Huw S Thomas, and then by headmistress Rhiannon Lloyd from Rhydywaun School. In early 2010, the board of governors announced that from September 2010, the former head of Rhydywaun School would take over from Rhiannon Lloyd. From September 2010, Alun Davies was headmaster prior to Mathew Evans joining the school in September 2020 as headteacher from Ysgol Gymraeg Ystalyfera Bro Dur.[2]
Pupil numbers at the school increased into four figures during the mid-1980s, necessitating the annexing of the buildings of the old Waterhall School in Fairwater to form the Ysgol Isaf (Lower School), which housed the first and second forms (later years 7 and 8) of the school from 1986. This split-site arrangement continued until the opening of Cardiff's second Welsh-medium comprehensive school, Ysgol Gyfun Gymraeg Plasmawr, in 1998, from which point the Llandaff North site again housed the entirety of Glantaf's pupils.
Education in Wales differs in certain respects from the systems used elsewhere in the United Kingdom. Ysgol Gyfun Gymraeg Glantaf is a Welsh-medium school, which means that all lessons except English language and literature should take place in the Welsh language. The social use of Welsh is also highly encouraged, in order to ensure the pupils' fluency in the language. Ysgol Glantaf presents sixth form students for the Welsh Baccalaureate examination.
The school's motto is Coron Gwlad Ei Mamiaith, which translates to 'A Country's Crown is Her Mother Tongue'. The school colours are light and dark blue.
The school's four houses are named after Welsh saints: Dewi (house colour: yellow), Dyfrig (green), Illtud (red) and Teilo (blue). The four houses annually compete in the『Gŵyl Glantaf』(Glantaf Festival), in which there is a day of sports and a day of singing, playing instruments, reciting and numerous other events in the theme of the Eisteddfod.
In 2008, 76% of pupils at GCSE (or equivalent) (ages 15 to 16) year achieved five or more A* - C grades at GCSE,[3] and 76% of pupils at A/AS level (or equivalent) (ages 17 to 18) achieved two or more A - C grades.[3]
