Herbert Smith is advising on the demutualisation of the London Stock Exchange.
The exchange's 298 member firms will vote on 15 March regarding proposals to turn it into a shareholder-owned company, with an estimated value of more than £400m.
Herbert Smith corporate partner Stephen Barnard is leading a six-strong team on the proposal.
Other partners involved are senior partner Edward Walker-Arnott and Colin Chamberlain, who is advising on shares issues.
Barnard says: "We have been doing work for the exchange for a few years and they asked us to get involved. It is changing a quasi-mutual company with A and B shares into a published company with ordinary shares and a 4.9 per cent limit on holdings."
Barnard is unwilling to discuss the legal issues involved in the transaction because of client confidentiality.
There is no share offering, and Herbert Smith is the sole law firm acting on the demutualisation.
Other advisers are stockbrokers Cazenove & Co, auditors PricewaterhouseCoopers and investment bank Schroders.