The Old King’s Club has been the way for former pupils of King's College School to keep in touch with each other and with their old teachers since 1884. It has often been said that the three pillars of the King's community are the School's staff, its governing body and the Old King's Club. The aim of the club is to promote the “honour and well-being” of its members and of the school. Social activities include dinners and get-togethers in London and further afield. The club runs successful rugby, football, golf, tennis, shooting and other sporting sections while the annual Careers Evening gives members the chance to offer advice to current pupils and to meet old friends. The annual Duel Day dinner provides an entertaining link to the foundation of King's in 1829.

Members are entitled to wear one of the club's ties, as well as its buttons and cufflinks.

The club is owned by its members and is independent of King's, but receives administrative and financial support from the school.

All former pupils of King’s College School are entitled to join the Old King’s Club, and normally join as Life Members. At this time, Life Membership is offered for free. Former pupils who wish to join are warmly invited to submit an application to the Honorary Secretary by completing this online form.

Annual membership is free and open to all King's past pupils.