Killefer held a variety of leadership roles at McKinsey & Company over the span of three decades until her retirement in 2013, serving a multitude of companies across consumer, retail, restaurant and technology industries. Currently a member of the boards of Cardinal Health, Inc. (since 2015), Taubman Centers, Inc. (since 2019) and Natura & Company (since 2020), Killefer previously served on the boards of Avon Products, Inc., National Trust for Historic Preservation, Partnership for Public Service, Computer Sciences Corporation, Advisory Board Company and CSRA, Inc. She has also held various roles within the government, including Assistant Secretary for Management, Chief Financial Officer, and Chief Operating Officer for the U.S. Department of Treasury from 1997 to 2000. Killefer then served as a member of the IRS Oversight Board from 2000 to 2005, including as Chair of the IRS Oversight Board from 2002 to 2004.