The Cabinet approved construction of Cashmere High School on 15 March 1954. Tender for the construction of the school, initially accommodating 600 pupils, opened on 1 June 1954 and closed on 6 July. After the initial tenders were rejected and fresh tenders were called, construction was let in late October to P. Graham and Sons Ltd for
£170,000. Construction of the school began on 26 October 1954.
Terry McCombs, a former Member of the
New Zealand House of Representatives who had served as
Minister of Education from 1947 to 1949, was appointed as the school's foundation headmaster in August 1955. Cashmere High School opened to students on 1 February 1956, with an initial intake of 190 third-form (now Year 9) students. The school was officially opened on 29 November 1956 by Minister of Education
Ronald Algie. Cashmere suffered moderate damage in the 22 February
2011 Christchurch earthquake, mainly from
liquefaction. On the day, the school had closed for instruction for the day at 12:00 pm due to the
Post Primary Teachers' Association, the main secondary school teachers' trade union, holding a paid union meeting that afternoon, meaning very few students and staff were on site when the quake struck at 12:51 pm. The school reopened on 14 March after the school buildings were inspected and deemed safe, and essential repairs and temporary fixes had been carried out. In the aftermath of the earthquake, the school played host to
Linwood College in a site sharing agreement while Linwood's severely damaged facilities were inspected and repaired. Cashmere used the site in the morning, while Linwood used the site in the afternoon for five months, until Linwood College moved back to its original site on 1 August. The current principal, John Stradwick, replaced Joe Eccleton in October 2024. ==Enrolment==