The school was founded by Cornish Methodists in 1880 as Truro College, a 'middle class' boys' school and moved to its present site in 1882. It grew under the headmastership of Herbert Vinter between 1890 and 1921. In 1904 it became one of the original Board of Management schools. In co-operation with the local authority, which awarded many county scholarships over the years, it quickly established and maintained a fine academic reputation. Under Dr.E.H. Magson, headmaster 1921-1946, academic standards were raised and the school's premises and facilities improved. Treliske was established as a preparatory school in 1936 (now Truro Prep School). Two of its former headmasters have been Vice-Presidents of the Conference: A. Lowry Creed (1962; headmaster 1946-1959)) and ??? (1987; headmaster 1959-1986). New playing fields and the Memorial Library (since relocated) was added in memory of the casualties in two World Wars. The Burrell Theatre was opened in 2002 by Sir Tim Rice. A new sports centre was opened in 2013 by a former pupil, Sir Ben Ainslie and named after him.
After a long period of debate the school reverted to full independence in 1976, following the withdrawal of the government's Direct Grant regulations. It became fully co-educational in 1990. Its records for 1980 contain a unique governors' resolution forbidding the construction of 'a second aircraft' - a cryptic tribute to an enthusiastic technology department. In 2017 there were 780 pupils in the main school and 240 in the prep. school, day pupils now outnumbering the boarders.
Among its former pupils are Bishop Joseph W. Hunkin, the Rev. Dr. W.P. Stephens, President of the Conference in 1998, David Penhaligon MP, Julia Goldworthy MP, the England rugby player John Kendall Carpenter, Olympic medal-winning sailor Ben Ainslie, actors Robert Shaw and John Rhys Davies, Roger Taylor from Queen, wildlife filmmaker Ellen Hussaiin, and the internationally famous baritones Benjamin Luxon and Alan Opie.