While the Provincial assemblies continued to meet after the founding of the Empire, their powers were all transferred to the Senate, and so senatorial decrees acquired the full force of law. The legislative powers of the Imperial Senate were principally of a financial and an administrative nature, although the senate did retain a range of powers over the provinces. The Senate could also regulate festivals and religious cults, grant special honors, excuse an individual (usually the Emperor) from legal liability, manage temples and public games, and even enact tax laws (but only with the acquiescence of the Emperor). However, it had no real authority over either the state religion or over public lands.

During the early Empire, all judicial powers that had been held by the Provincial assemblies were also transferred to the Senate. For example, the senate now held jurisdiction over criminal trials. In these cases, a Consul presided, the senators constituted the jury, and the verdict was handed down in the form of a decree and while a verdict could not be appealed, the Emperor could pardon a convicted individual through a veto. Each province that was under the jurisdiction of the Senate had its own court, and, upon the recommendation of a Consul, decisions of these provincial courts could be appealed to the Senate.