The Conference dates from 1869 when Edward Thring, Headmaster of Uppingham, asked sixty to seventy of his fellow headmasters to meet at his house to consider the formation of a "School Society and Annual Conference". Fourteen accepted the invitation, and twelve were present for the whole of the initial meeting: Thring himself, George Blore (Bromsgrove), Albert Wratislaw (Bury St Edmunds), John Mitchinson (The King's School, Canterbury), William Grignon (Felsted), Robert Sanderson (Lancing College), George Butler (Liverpool College), Augustus Jessopp (Norwich School), William Wood (Oakham), Steuart Pears (Repton), T. H. Stokoe (Richmond), Daniel Harper (Sherborne), and James Welldon (Tonbridge). John Dyne (Highgate School) attended on the second day, and Alfred Carver (Dulwich College) did not turn up. From that date there have been annual meetings. It changed its name from the "Headmasters' Conference" to the "Headmasters' and Headmistresses' Conference" in 1996. The current Chairman is Christopher King, Headmaster of Leicester Grammar School, and the current general secretary is William Richardson.
Membership of the HMC is often considered to be what defines a school as a public school in England and Wales. Not all private, independent schools are in the HMC; in particular, many notable girls' schools are not members, partly because historically the HMC was for boys' schools only. Today HMC's membership includes boys', girls' and co-educational schools.