Judge O'Malley was appointed to the Superior Court of Contra Costa County in 1998. She was supervising judge of the court’s criminal division from 2005 to 2009 and was elected to a two-year term as presiding judge in 2008. She began her legal career as a law clerk for the district attorney’s offices in San Francisco and Contra Costa Counties (1983–1985). She later served as deputy district attorney for Contra Costa County. Judge O’Malley was initially appointed to the council on Jan 1, 2011, to complete the last few months of another council member’s term. Judge O’Malley previously served as a nonvoting advisory member, as a result of a one-year term as chair of the Trial Court Presiding Judges Advisory Committee. Judge O’Malley has served on the Trial Court Budget Working Group since 2009 and is a member of the Advisory Committee on Financial Accountability and Efficiency. She is a former member of the council's Executive and Planning Committee. In addition, she has served on the Advisory Committee on Criminal Jury Instructions, the Public Access Rule of Court Working Group, and the Judicial Recruitment and Retention Working Group. She is an instructor at the B. E. Witkin Judicial College, New Judge Orientation, and the Continuing Judicial Studies Program of the Center for Judicial Education and Research (CJER) and serves on the CJER Criminal Law Education Committee and Criminal Law Curriculum Committee. In Nov 2012, she was appointed by the Chief Justice as a member of the Trial Court Funding Workgroup, a judicial and executive branch working group evaluating the progress of statewide funding for trial courts.