Phil de Cristo, president of investments at Mercer, is to resign effective March 31, spokeswoman Alayna Francis said.
Mr. de Cristo plans to take some time off and consider his options, Ms. Francis said.
After Mr. de Cristo leaves the company, Mercer will formally combine its investment and retirement consulting practices into a new wealth business.
Andrew Kirton, chief investment officer for EuroPac, will become global chief investment officer for Mercer Investments in January.
Also in January, Tom Murphy, head of Mercer's DC and financial wellness unit in the U.S., will become wealth business leader for the U.S.
Jacques Goulet, previously global president for Mercer's retirement and health businesses, will lead the wealth and health businesses globally for Mercer.
Mercer has more than $9 trillion in assets under advisement.
