Steel was born in Seoul, South Korea. Her father was born in Shanghai to Korean expatriate parents. Steel was educated in South Korea, Japan, and the United States. She holds a degree in business from Pepperdine University and an MBA from the University of Southern California; she is fluent in Korean and Japanese.
Steel's interest in tax issues began at an early age when she watched her mother fight what they believed was an unwarranted Board of Equalization tax bill. As an immigrant small business owner, Steel's mother lacked the resources to successfully fight the massive state agency and reluctantly acceded to the Board's demands.
Steel began her community involvement as a commentator on Radio Seoul from 1993 until 2007. She has also volunteered for several youth organizations, including Options House, a local emergency shelter helping runaway children, and the Coalition of Brothers and Sisters Unlimited, an African-American after-school program.
Steel and her husband, former California Republican Party Chairman and current Republican National Committee Committeeman from California Shawn Steel, have been married since 1981 and have two daughters, Cheyenne and Siobhan. They live in Surfside, California.
From 2001-2003, Steel served on the President's Advisory Commission on Asian Americans and Pacific Islanders under President George W. Bush, the California World Trade Commission, the Los Angeles County Department of Children and Family Services, and the Los Angeles Airport and Fire Commissions. She was later appointed to the White House Conference on Aging under President George W. Bush.
Her public policy experience includes service as a member of the California Orange County Deputy District Office: Korean American Community Commission and member of the Tax Advisory Committee for the State Board of Equalization.
Outside of government, she has also been active in Republican Party positions, serving as a board member for the Korean American Republican Association and having been an honorary chair of Governor Arnold Schwarzenegger's 2006 Gubernatorial Campaign.
Steel was elected to the California State Board of Equalization in 2006 when Republican incumbent Claude Parrish ran unsuccessfully for state Treasurer. Throughout her tenure, she served as the country’s highest ranking Korean American officeholder and California's highest ranking Republican woman. She represented more than eight million people in the 3rd district, which then included the entirety of Imperial, Orange, Riverside, and San Diego counties, as well as portions of Los Angeles and San Bernardino counties. Steel promised to protect taxpayers from the overbearing government that her family encountered. A signatory of the Taxpayer Protection Pledge, she promised to oppose all new taxes and tax increases, and when adjudicating tax appeals, presume a taxpayer is innocent until proven guilty.
In 2011, she was elected Vice Chair of the Board of Equalization.
In 2014, she ran successfully to become a member of the Orange County Board of Supervisors representing the 2nd district, easily defeating state Assemblyman Allan Mansoor. She served as Vice Chair of the board in 2016 and was unanimously elected to serve as the Chairwoman for 2017.