Jeremy Horner oversaw the management changes after David Langdon was bought by Aecom last year.
The reasons behind his sudden departure after 20 years at the firm are still unclear.
Aecom said Bob Pell now becomes global chief executive of its programme, cost and consultancy practice, which includes Davis Langdon.
Management changes at Davis Langdon since the Aecom takeover have seen a raft of senior partners leave the firm.