For much of the history of the federal courts, commissioners assisted federal judges and provided the federal government with local officers to support the enforcement of specific laws. In 1793 Congress authorized federal judges to appoint "discreet persons learned in the law" to take bail in federal criminal proceedings. The statute allowed officers of the federal courts to assume responsibilities that the Judiciary Act of 1789 had vested in local magistrates and justices of the peace. In 1812 Congress authorized these court-appointed federal officers, who were no longer required to have legal training, to take affidavits in cases brought in the circuit courts. An act of 1817 referred to the officers as "commissioners" and authorized them to set bail, to take affidavits in civil cases brought in the district courts, and to take the depositions of witnesses who were unable to appear in federal court. In an 1842 act, Congress granted commissioners the same authority over federal criminal processes as it formerly had granted to state court magistrates and justices of the peace, including the power to arrest and imprison the accused.

Over the remainder of the nineteenth century, Congress periodically expanded the powers of commissioners to enforce federal laws, particularly in cases when state officials might not be consistent or reliable in their enforcement. The Fugitive Slave Act of 1850 granted commissioners jurisdiction concurrent with that of federal judges to authorize the apprehension of fugitive slaves. Commissioners were called on to enforce the Civil Rights Act of 1866, which extended citizenship to formerly enslaved people. Under the Chinese exclusion acts of the 1880s, commissioners had the same authority as judges to order the removal of persons of Chinese descent who were unlawfully in the United States.

Circuit courts were authorized to appoint as many commissioners as necessary, and in 1878 the Department of Justice estimated that nearly 2,000 commissioners served the federal courts. Most commissioners were lawyers who carried out their judicial responsibilities while pursuing their own practice. Federal court officers, such as clerks, might also serve as commissioners, as did officers of state and local courts. By the late-nineteenth century, the large number of commissioners and the reliance on an irregular schedule of fees for compensation provided opportunities for abuse in the reporting of fees and led to calls for congressional reform of the commissioner system.

In 1896 Congress established the formal office of "United States Commissioner," and transferred the power to appoint commissioners from the circuit to the district courts. United States Commissioners were appointed for terms of four years, but could be removed by the district court at any time. Congress also established a uniform fee schedule for the compensation of commissioners and prohibited other court officers from serving as commissioners. Responding to the increased volume of federal judicial business, Congress in 1940 enacted a measure that permitted judges of the district courts to delegate to their commissioners the authority to try and to sentence individuals charged with petty offenses on federal reservations. Defendants had the right to request a trial in the district court and could appeal a commissioner's decision.

Dissatisfaction with the fee system, the lack of uniform standards for appointment, and the desire to expand the judicial responsibilities of the commissioners contributed to growing calls for reform of the office. A series of Judicial Conference studies and congressional hearings eventually led to approval of the Federal Magistrates Act of 1968, which abolished the office of United States Commissioner and substituted for it the office of United States Magistrate (later Magistrate Judge).

Further Reading:
Lindquist, Charles A. "The Origin and Development of the United States Commissioner System," American Journal of Legal History 14 (January 1970): 1-16.