Llanhari is one of the original Welsh mediumsecondary schools in the area, having opened in 1974. It followed Ysgol Gyfun Rhydfelen in leading the way in Welsh medium education in South Wales. In 1974, the school was located in the county of Mid Glamorgan and had a huge catchment area from Tonteg and Cardiff in the east, all the way to Porthcawl and Maesteg in the west. It became popular very quickly and grew in numbers, becoming oversubscribed. Within a few years, it was decided that South Glamorgan pupils would be educated in their own county and in 1978, Ysgol Gyfun Gymraeg Glantaf opened in Cardiff. On 6 June 2011, it was publicly announced that from 2012 the school would incorporate a primary unit and become a 3-18 school. On 3 September 2012, the Primary Unit was opened and the school was formally designated a 3-18 school with the new name of Ysgol Llanhari. Mrs Catherine Webb is Assistant Head with responsibility for this unit.
Feeder schools
Llantrisant, Tonyrefail, Dolau and the primary section of Ysgol Llanhari are the current feeder schools to the secondary section at Llanhari. Before the opening of Ysgol Gyfun Gymraeg Llangynwyd in 2008, the following schools also fed Llanhari with pupils from the county of Bridgend: Ysgol Y Ferch o'r Sger, Ysgol Bro Ogwr, Ysgol Cynwyd Sant and Ysgol Gymraeg Cwm Garw. These pupils are now educated at Llangynwyd, within their own county.
Headteacher
To date, Ysgol Llanhari has been led by five heads. Mrs Rhian Phillips is the current headteacher at the school. She succeeded Mr Meirion Stephens, who served as head of Llanhari from January 2008. He was preceded by Miss T Anne Morris, who took over in 2003. Prior to this, Mr Peter Griffiths, father ofIoan Gruffudd, star of such films as Fantastic Four and Wilde served as head from 1989. The original head when the school opened in 1974 was Mr Merfyn Griffiths. Since 2014, Ms Meinir Thomas has served as deputy Headteacher, with Ms Catherine Webb and Mr Geoffrey Howell serving as assistant head teachers. As of 2019, Mr Marc Evans, has been promoted to the role of assistant Headteacher, alongside Ms Webb and Mr Howell.
Heads of Year
Miss Angharad Morgan has responsibly for Year 7 and 8 currently. Mrs Elen George is the current Head of year for Years 9 and 10 and Mr Stephen Wilshaw is Head of Year for Years 11, 12 and 13.
Exam results
Examination results have consistently improved since 2008. In 2012, 75% of pupils attained grades A*-C in all A-Level subjects sat, and 97% were awarded grades A-E in all subjects. At GCSE, 74.2% of all grades awarded were A*-C and 74.6% of students attained the 5 A*-C benchmark.
