Charlemont High School was founded by the late John Bernard Stephenson, who was affectionately called “Jack Stephenson,” who was a former Member of Parliament for North St Catherine. The idea came about as a result of concerns expressed by parents in the area whose children had to attend schools outside the area, as far as Kingston and Claremont in St Ann. The land was bought from the late Custos McGrath, with funds for the building and infrastructure coming from businesses and service clubs in North St Catherine including Alcan Jamaica Limited, the Lions Club, the United States and the Jamaica Citrus Growers Association. The St Catherine Garden Club landscaped the school grounds.
The school admitted its first students on September 11, 1978. There were three first forms and three second forms accommodating a total of two hundred and forty students. There were twelve teachers including the principal, Mr. Ruel Forsythe. Mr. Forsythe left at the end of 1979 and was succeeded by Mr. Donaldson Bernard in September of the same year. In 1981 the school was expanded with funds from the Norwegian Government. This was the start of phase two of the building program when several classrooms and laboratories were built and the Home Economics center expanded.