In her new position, she will be responsible for client satisfaction, retention and growth in providing recordkeeping services to large employer-sponsored 401(k) defined contribution and benefit plans.

"Mary understands what it takes to be a leader in the large and mega plan arena," said Linton in a statement. "Having previously worked with her for many years, Mary's deep industry experience, passion for her work and expertise serving sponsors of all sizes will benefit our clients as she continues to build on the strong relationships that already exist."

Witherow previously worked at Fidelity Investments for nearly 15 years.

There she held several leadership positions in the firm's retirement business, first in large corporate relationship management and later as the senior vice president and head of relationship management for the advisor-distributed market—that latter a division that covered both the small/mid- and large-market spaces.

Prior to that, Witherow worked as an attorney for the U.S. Department of Labor, where she served as counsel for ERISA and was recognized on two separate occasions with the Secretary of Labor's Exceptional Achievement Award for litigation.

She holds a B.A. and a J.D. from the University of Oklahoma, and is a registered representative with a Series 6, 7, 24, 26 and 63 licenses.