Marymount, originally known as Holy Spirit School for girls, was founded by the Maryknoll Sisters. The school opened on 10th January 1927 at Robinson Road with only 8 classes of students sharing 4 tiny classrooms. In 1930, the school moved to the building at 140 Caine Road which provided 7 classrooms. By 1941, it offered a complete course of studies leading to matriculation. The school was closed during the war. It re-opened as Maryknoll School in 1948.

As the school continued to expand, a school building with improved facilities became necessary. In October 1957, the school moved to its present location in Happy Valley and was renamed Maryknoll Sisters School. Initially, the building housed both Secondary and Primary Sections. It was not until 1961 that the Primary School occupied the premise at Tai Hang Road. During the school year 1978-79, after 52 years of devoted service, the Maryknoll Sisters handed over the sponsorship of the school to the Columban Sisters.

As of September 1983, the name of the school was changed to Marymount Secondary School and Marymount Primary School respectively. By 1993, to meet the needs of increasing student population in the Secondary School, the Columban Sisters turned over to the use of the school the remaining convent area on the fourth floor.

In 1996, the Columban Sisters initiated the transfer of the sponsorship of the school to the Christian Life
Community (CLC), the process of which was completed by September 1997. The CLC is an international Catholic lay community with a keen interest in education and commitment to the service of youth. The CLC has pledged to preserve the same school spirit, foster the traditions and continue to provide quality education at Marymount.

The Secondary School operated up to 29 classes with over 1000 students until 1998, offering arts, science and social disciplines up to Form 7. With the restructuring of the school, the total number of classes will be at 26 by the year 2003. The Primary School operates 24 classes and has about 900 students.