Kloof High School was founded in 1960. This being after two parents of school-going children, Mr Grant Loudon and Professor Desmond Clarence, did a statistical survey in 1959 in order to establish the need for a high school in the upper Highway area. The school opened in 1960 with 127 pupils, on a temporary site which is now the top playing field for the Kloof Senior Primary School. In order to make the school viable, Standard 4 and 5 pupils were also housed on this site and were included in the total of 127 pupils.
Mr G M N Goodwin was the first Headmaster and he was assisted by five full-time and four part-time teachers. Before the school was a year old, Mr Goodwin was transferred to Eshowe High School. Mr Blake, the vice-principal, acted as principal until Mr J F Dixon arrived as the second Headmaster in January 1962. At the end of that year he left and the then vice-principal, Dr G S Jackson acted as principal for the next two terms. The first two Headmasters were at the school for a year and a half between them, the next two Headmasters were at the school for just under 25 years.
The first annual Sports Day was held at the Luther Field on 3 September 1960. The pupils were organised into 3 houses named after neighbouring streets – Dan Pienaar, Buckingham and Emolweni. On St Valentine's Day 1961, 28 children were taken to the Durban City Hall after school to attend a musical concert by the Durban Municipal Orchestra. Towards the end of that year almost the whole of the school took part in a concert in St Agnes Hall; Standard 6, which was then the senior class, put on a play "The Story of the Willow Pattern Plate". The first inter-school sports competitions took place in 1962 when the pupils participated in the Co-Educational Secondary School Swimming Gala in March and the Inter-High School Athletic meeting in September.
The school grew quickly under the third principal, Mr Dudley Barton, who succeeded Mr J F Dixon in 1963. Construction had begun on permanent buildings in 1963 and by mid-1964 the pupils of Standards 6 to 9 were able to move into their new classrooms. For some time the prefabs remained on the top hockey field while further building continued. In 1965 the first Standard 10 class wrote the Matriculation examinations and the present school houses, Churchill, Founders and Keller were established.
In 1969, Mr T Gerdener, the then Administrator of Natal, officially opened the school. By then there were 524 pupils and 26 teachers, a further classroom wing including an Art room and Library had been added and a school hall where "William Shakespeare" by Clemence Dane was produced by Mrs Barton. During the July holidays of that year the first sports tours were undertaken with the 1st Hockey XI touring the Eastern Cape and the 1st Rugby touring Rhodesia (now Zimbabwe). The faith of the founders had been justified and a coat of arms was designed by Mr Alan Woodrow including the motto: "In hoc signo vinces" (In this sign (the cross) you will conquer).
Mr Barton retired in 1978 and was succeeded by Mr H M Puzey under whom the school continued to grow. Further classrooms were built and the school proudly boasts a chapel, computer and video centre, air-conditioned conference room, a drama studio and clubroom for past students, parents and staff.
On the sports front, provincial and, on occasion, national honours, were earned in swimming, (the school now had a swimming pool), cricket, hockey, athletics and tennis – some of the varied sporting activities offered at the school. Academic excellence was encouraged and under Mr Hugh Deane (principal from 1989 to 1994) teachers were encouraged to be creative in their teaching methods, motivated in regular workshops wherein thinking skills, interpersonal skills, group dynamics and fitting the child for a fast changing society, were among subjects presented. To achieve this the Media Centre was upgraded. The school serves the community, being used for church services on Sundays, Argus Community School in the afternoons and evenings and hosting several cultural functions.
In 1993 Kloof High elected to become a state-aided school, a Board of Governors replacing the Management Council. The Board of Governors is directly responsible for the management of the school, in collaboration with the educators, with direct control of appointment and finances.
In January 1995 Mr Deane was succeeded by Mr David Seager who was Headmaster until March 2005. Mrs Dawn Lefort was appointed Principal in January 2011.