OATH was established by Executive Order No. 32 in 1979, to professionalize the administrative adjudication process serving New York City government. OATH was made a Charter agency in 1988, as part of the Charter revisions which enacted the . Among CAPA's primary reforms was the adoption of standards for the conduct of administrative proceedings and the establishment of OATH as the first municipal central tribunal in the country independent from the agencies that refer cases to it.
Removing adjudications from within agencies was a primary objective of the Charter revision. OATH Trials' Administrative Law Judges (ALJs) are subject to the same rules of conduct and ethics that apply to all members of the New York State Judiciary (22 N.Y.C.R.R. § 100). Moreover, all ALJs and OATH Hearing Officers are also subject to the Rules of Conduct for Administrative Law Judges and Hearing Officers of the City of New York (Appendix -Chapter 48 of the Rules of the City of New York).
Initially, OATH's caseload consisted of mostly disciplinary cases brought by City agencies against civil service employees. With the 1988 Charter revisions giving OATH general jurisdiction, the types of cases referred to OATH substantially expanded. As a result of a rule modification in 2015, OATH has expanded to include other administrative tribunals. However, the original tribunal, now referred to as OATH's Trials Division, continues to perform its Charter function of handling a wide variety of complex administrative proceedings in a fair and impartial manner.