The King's School was founded in 1502 within the Church of St Michael and All Angels, Macclesfield. It was re-founded by Edward VI in 1552 as the "Free Grammar School of King Edward VI", moving to its current location on Cumberland Street in 1844.
The school operated as a direct-grant school and offered scholarships for boys from state elementary schools from 1926 until 1966, when its application to continue as a direct grant grammar school was refused and it became fully independent.
The boys' junior school was opened in 1947. In 1993 girls from age 11 to 16 were admitted and housed with co-educational juniors, and later infants, at the old Macclesfield High School site on Fence Avenue. The Sixth Form had been co-educational since 1986.
King's School's 2020 development plans are designed to close the two existing school sites in Macclesfield and open a new single site school in Prestbury, near Macclesfield. The development plans involve selling off the two existing school sites for housing development to fund the new school site. The school acquired greenbelt farmland adjacent to its Fence Avenue site for which it subsequently sought planning permission in order to develop the existing school site and the farmland for housing. Planning permission was granted to the school to build more than 250 houses on the greenbelt land in Macclesfield in July 2016.The proposed new school will also be built on green belt land in nearby Prestbury. Planning permission for all sites was confirmed when the Secretary of State declined to call in the plans for further scrutiny in September 2016.
The school follows the National Curriculum for GCSE in Years 10-11 and A-Levels in the sixth form. In 2012, pupils achieved A*/A in 41% of all exams and A* - B in three quarters of exams. Pupils achieved the best-ever GCSE results in 2012 with 33% of grades at A* grade, more than 63% of grades at A*/A and 86% at A* - B grade.