He replaces Don Cruickshank, and will take a massive salary cut in his new role.
A former managing director at BP, Gibson-Smith earned a package in the region of £2.8m, but can expect a salary of £250,000 for his two-day-a-week non-executive role.
Prior to his appointment to the LSE, Gibson-Smith was chairman of Nats, the air traffic control service.
Mark McMullen joins the private client services team from Smith & Williamson
Merger between Clear & Lane Chartered Accountants and Magma Chartered Accountants was finalised on 3 February
BDO has taken its new partner intake to 23 during the first half of its financial year, including the appointment of five partners in five weeks
The firm reports 7.6% global fee income growth for the year ending 31 December 2016