|Motto||Gorau gwaith gwasanaeth ('[Your] best work is to serve')|
|Local authority||Rhondda Cynon Taf|
|Chair||Mr Ceri Morgan|
|Head||Mrs. Rhian Phillips|
|Age||3 to 18|
|Colour(s)||Black and Red|
Llanhari is one of the original Welsh medium secondary 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.
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.
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 of Ioan 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.
Heads of Year
Miss Angharad Morgan is the current Head of Year for Year 7 and 8. 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.
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.
Notable former/current pupils
- Mererid Hopwood, poet and academic - first woman ever to win the chair at the National Eisteddfod of Wales
- Manon Antoniazzi, Chief Executive and Clerk to the National Assembly for Wales
- Garnon Davies, actor (Hollyoaks)
- Bethan Ellis Owen, actress (Pobol y Cwm)
- Shelley Rees, actress (Pobol y Cwm)
- Gareth Wyatt, Welsh international rugby player
- Scott Gibbs, Welsh international rugby player
- Guto Harri, former BBC Chief Political Correspondent, Communications Director for the Mayor of London's administration
- Betsan Powys, journalist, and former head of BBC Radio Cymru
- Rhys Williams, professional athlete, specialising in the 400 m hurdles
- Aled Siôn Davies, Paralympian
- Rhys Rubery, student who tragically died 12th July 2016. The charity RR81 was set up after his death to help fund projects for the school.
- Ysgol Llanhari website. Accessed 26 December 2015.
- Carrie Evans, 'Ysgol Llanhari celebrates 40 years of Welsh language education', Wales Online, 30 October 2014. Accessed 26 December 2015.
- "Inspection under Section 10 of the School Inspections Act 1996" (PDF). Estyn. Retrieved 26 April 2008.
- Merfyn Griffiths, 'Growth in Secondary Education in Mid Glamorgan', in Iolo Wyn Williams (ed.), Our Children's Language: The Welsh-medium Schools of Wales 1939–2003 (Talybont, 2003), p. 115; retrieved 23 September 2013.
- My Local School: Ysgol Llanhari; retrieved 23 September 2013.
- "BBC Wales public affairs head moves up to UK-wide role". BBC. Retrieved 13 August 2017.
- "Pobol Y Cwm Characters". Archived from the original on 13 March 2008. Retrieved 2 August 2008.