The Freemasons will allow women to be members for the first time in their history, but only if they were men at the time of joining.
The secretive group released a report on its “gender reassignment policy” which also said that women who had transitioned to men would also be allowed to join.
After consulting a judge, the organisation warned that expelling masons for transitioning was “unlawful discrimination”.
A message sent to members said: “It is important that any situation involving gender reassignment of a Freemason is treated with the utmost compassion and sensitivity and that the individual is supported throughout the process.
“If a Freemason who is a member of UGLE [the United Grand Lodge of England] wishes to change gender and become a woman we expect that the Freemason would receive the full support of their brethren.”
Michael Baker, the director of communications of the United Grand Lodge of England, the organisation’s governing body, said: “While there has been no general request for guidance on gender reassignment, questions on the subject are likely to become increasingly common in future, and now appears to be an opportune time to issue general guidance to our members.
“It should also be noted that people who the law classifies as female will still be exempt from membership of UGLE. They may, of course, become members of the two female-only grand lodges – the Order of Women Freemasons and the Honourable Fraternity of Ancient Freemasons – both of whom refer to members as brothers.”
Often shrouded in mystery, the Freemasons are one of the world’s oldest and largest non-religious, non-political organisations, with branches across the world.