A promagistrate is a person who acts in and with the authority and capacity of a magistrate, but without holding a magisterial office. A legal innovation of the Roman Republic, the promagistracy was invented in order to provide Rome with governors of overseas territories instead of having to elect more magistrates each year. Promagistrates were appointed by senatus consultum; like all acts of the Roman Senate, these appointments were not entirely legal and could be overruled by the Roman assemblies, e.g., the replacement of Quintus Caecilius Metellus Numidicus by Gaius Marius during the Jugurthine War.
Promagistrates were usually either proquaestors (acting in place of quaestors), propraetors (acting in place of praetors), or proconsuls (acting in place of consuls). A promagistrate held equal authority to the equivalent magistrate, was attended by the same number of lictors, and generally speaking had autocratic power within his province, be it territorial or otherwise. Promagistrates usually had already held the office in whose stead they were acting, although this was not mandatory. Other promagistrates include the procurator (acting in place of a curator).