The role of the Orange County Public Defender's Office is to provide quality representation to indigent clients in an efficient and cost-effective manner. These services are provided through three independent units, the Public Defender’s Office, the Alternate Defender's Office, and the Associate Defender's Office, all of which operate under the administrative supervision of the Public Defender, Martin Schwarz. The three segments employ approximately 211 attorneys and approximately 196 additional support staff (including administrative staff, investigators, investigative assistants, clerical staff, IT personnel, and paralegals).

The Public Defender’s Office operated as a single public law firm for 50 years, from its establishment on February 16, 1944 until January 10, 1995. On that date, at the direction of the County Board of Supervisors, the office split into three separate segments. Division into three units was in response to the county bankruptcy and was designed to save money by shifting thousands of “conflict cases” from costly court-appointed private counsel to the Offices of the Public Defender. As a result of the segmentation more than $6 million was saved in the first full year, with savings currently exceeding $7 million annually.

Milestones in the history of the Office include: the first Public Defender, Nick Meyer, worked part-time initially in the position, but two years later Sam Dreizen was hired, part-time, as the first "deputy" public defender. A change in statutory law in 1949 added preliminary examinations to the duties of the public defender. In 1956 the attorney staff of Nick Meyer, Dick Sullivan and Frank L. Williams, Jr., handled 416 felony cases. Dick Sullivan became Public Defender in 1956 upon the death of Nick Meyer, and Gene Langhauser became a deputy public defender. In 1957 mental health cases were added by statute to the Public Defender duties, and in 1958 John Bond was hired as the first staff investigator. In 1960 Frank Williams, Jr. became Public Defender and in 1961 juvenile cases were added to the list of duties, with the attorney staff increased to five. In 1965 the Public Defender began handling misdemeanor cases for the first time, and by 1966 there were 14 staff attorneys. By 1968 caseloads were between 8,000 and 9,000.

The 1970s saw an increased urbanization in Orange County and with it came a rise in criminal prosecutions, and a larger Public Defender's Office. Upon the untimely death of Frank Williams, Jr. in 1981, Ron Butler became Public Defender. Carl C. Holmes then served as Public Defender until his retirement in January 2003, when Deborah A. Kwast began her service as the head of the approximately 370-person department.

On August 2, 2011, Deborah Kwast retired and Frank Ospino was appointed Interim Public Defender. On January 27, 2012, Frank Ospino was appointed Public Defender as a result of an extensive recruitment. On December 30, 2015, Frank Ospino retired and Sharon Petrosino was appointed Interim Public Defender. On June, 2016, after an extensive recruitment, Sharon Petrosino was unanimously appointed by the Board of Supervisors to be the Public Defender. On July 2, 2020, Sharon Petrosino retired and Martin Schwarz was appointed Interim Public Defender. On May 11, 2021, after an nationwide recruitment, Martin Schwarz was unanimously appointed by the Orange County Board of Supervisors to the Public Defender.