A Roman governor was an official either elected or appointed to be the chief administrator of Roman law throughout one or more of the many provinces constituting the Roman Empire.

The generic term in Roman legal language was rector provinciae, regardless of the specific titles, which also reflects the province's intrinsic and strategic status, and corresponding differences in authority.

By the time of the early Empire, two types of provinces existed—senatorial and imperial—and several types of governor would emerge. Only proconsuls and propraetors fell under the classification of promagistrate.

The governor was the province's chief judge. He had the sole right to impose capital punishment, and capital cases were normally tried before him. To appeal a governor's decision necessitated travelling to Rome and presenting one's case before either the praetor urbanus, or even the Emperor himself, an expensive, and thus rare, process. An appeal was unlikely to succeed anyway, as a governor wouldn't generally take the chance of convicting someone contrary to the Emperor's wishes. The governor was also supposed to travel across his province to administer justice in the major towns where his attention was required.

Finally, and most importantly, he commanded the military forces within the province. In the more important provinces, this could consist of legions, but elsewhere, there were only auxiliaries. As a part of his standing orders, the governor had the authority to use his legions to stamp out organized criminal gangs or rebels in the area without need for the Emperor's or Senate's approval.

Every governor had at his disposal a diversity of advisors and staff, who were known as his comites (Latin for "companions"); the number of these depended on the governor's social standing and rank. These comites would serve as the governor's executive council, with each supervising a different aspect of the province, and assisting the governor in decision making. In the provinces with a significant legionary presence, the governor's second-in-command was usually a quaestor, a man elected in Rome and sent to the province to serve a mainly financial role, but who could command the military with the governor's approval. In other provinces governors themselves appointed non-magistrate prefects or procurators to govern a small part of the province and act as their second-in-command.

During the era of the Roman Republic, the council was in charge of appointing governors to Rome's provinces. This was done by appointing promagistrates to serve, either by random casting of lots or by senatus consultum (advice of the Senate); however, these appointments were not formally binding on a legal basis and could be nullified by Roman assemblies.

Initially, a governor or general's title – pro praetore or pro consule - was determined by the last held previous urban magistracy: that is, former praetors were prorogued in place of a praetor (pro praetore) and former consuls were pro consule. This system, however, started to break down after private citizens were given commands in Spain pro consule during the Second Punic War. By the late republic, praetors were almost always prorogued pro consule. However, the provinces that ex-praetors were assigned – regardless of formal title – were usually the more tranquil ones, where chances of revolt or invasion were small. Provinces where imminent military campaigning was expected were instead assigned to recent consuls.