Andrew Kirton, chief investment officer for Mercer's wealth management business, will leave the firm in March.
Mr. Kirton will assist in the transition of his duties before "taking time to enjoy interests outside finance," spokeswoman Alayna Francis said in an email.
Four existing Mercer executives will assume Mr. Kirton's duties: Deb Clarke, global head of investment research; Donn Cox, alternatives business leader; Hooman Kaveh, global chief investment officer for delegated investment solutions; and William Muysken, global chief investment officer for alternatives.
In other executive moves within the investment consulting firm's money management unit, Graham Pearce was named global segment leader for Mercer's defined benefit plan client group. Mr. Pearce was global consulting leader in the multinational client group, Ms. Francis said.
Mr. Pearce replaced Benoit Hudon who was appointed U.K. wealth leader. Ms. Francis said the position is new.
Troy Saharic assumed the position of global segment leader for defined contribution and master trusts. His former role was U.S. wealth sales leader.
Messrs. Pearce and Saharic assumed their new roles from Renee McGowan who was global leader for defined contribution and individual wealth and was named CEO for the Asia region on Nov. 1.
Ms. Francis said Mr. Saharic's duties were assigned to others and his former position was eliminated.
Ms. Francis could not immediately provide information about replacements within Mercer for Mr. Pearce and Ms. McGowan.
"We are focused on aligning our talent to support our clients' evolving needs and to embrace and help lead innovation in the market," Rich Nuzum, president of Mercer's wealth management business, said in a news release.