The arrival of Mr Geary, 43, comes as Clifford Chance opens its 23rd office - and second in Vietnam - in Ho Chi Minh City.
The firm says his appointment as head of business development is a clear signal that senior partner Keith Clark and managing partner Geoffrey Howe intend to strengthen the management capabilities of the firm's 229 partners.
"International law firm partnerships have still to prove that their business development capabilities match those of the world's top companies," says Mr Geary. If Clifford Chance is to succeed against aggressive competition - particularly from US firms - it needs to master this area, he says.
Mr Clark says Mr Geary's role will be to "enhance each partner's ability to anticipate, and respond quickly and correctly, to market and client developments".