Mary O. Simmons is a born-and-raised Nevadan who grew up in Ely before attending the University of Nevada, Reno. She earned her bachelor's in business administration in accounting in 1978.

Simmons has worked for NV Energy in Reno since 1985, and currently serves as vice president, business development and community strategy. She was previously the vice president, rates and regulatory affairs; controller; and director of water policy and planning. Simmons is secretary for NV Energy's charitable foundation, and has served on the boards for the Economic Development Authority of Western Nevada (EDAWN), the Reno Philharmonic and the Great Basin National Park Foundation. Simmons was named a Foundation Trustee in 2013 where she has served as chair in 2015 and has served on the Nominating and Audit and Finance Committees.  

During Simmons' time with NV Energy, her company has supported scholarships in business, accounting, journalism, environmental science and engineering, and provided support for the renewable and sustainable energy program.

Simmons and husband, Reed, are members of the Alumni Association and the Silver and Blue Society, and are supporters of KUNR, Wolf Pack Athletics, and the College of Business.