Prior to that, she was the Lillian L. Moehlman Bascom Professor, School of Nursing and College of Engineering, at the University of Wisconsin–Madison.

She developed ComputerLink, an electronic network designed to reduce isolation and improve self-care among home care patients.

[citation needed] Brennan is the National Program Director of Project HealthDesign, a Robert Wood Johnson Foundation-funded initiative designed to stimulate the next generation of personal health records.

As of June 2009, Brennan was a theme leader of the Living Environments Lab at the Wisconsin Institutes for Discovery, researching home health care technologies using virtual reality and simulation technology.

[3] In 2016, she was appointed director of the National Library of Medicine, where her term started in August 2016.