The Galactic Senate, also referred to as the Republic Senate, Galactic Congress, Republic Congress, or Old Senate (during the time of the New Republic), was the legislative and executive branch of the Galactic Republic that was located on Coruscant. Its primary duties were to mediate any disputes between star systems, worlds and cultures, to regulate trade between systems, to protect and care for citizens in need and to provide mutual defense in face of threats to the Republic.
The Galactic Senate was a place where all the Republic's elected and appointed senators and representatives from the farthest reaches of the galaxy would discuss major problems and come to decisions. The Galactic Constitution invested the Senate with the power to regulate trade, maintain maps of the galaxy's hyperspace routes, and to maintain the Republic's military. It was still a relatively weak body at the end of the Old Sith Wars. Following the Ruusan Reformation, a large amount of power was removed from the Supreme Chancellor and granted to the Senate, which although resulting in greater regional involvement in galactic politics, also resulted in increased gridlock and corruption. One of the privileges a Supreme Chancellor still possessed was his or her ability to call an Extraordinary Session.
The Senate's role changed somewhat over the centuries. As of the Old Sith Wars it played a slightly more passive role regarding internal affairs. While recognized as the central government of the Republic and deferred to in matters of galactic policy, the Senate's power over many members was more that of a mediator than a ruling body. Negotiation and coercion were staples of its activities.
Before the start of the Clone Wars, the Senate suffered a shutdown, with corporations controlling it. The majority of the senators around the time of the Invasion of Naboo became corrupt, changing their affiliations based on their own interests in mind. Eventually, through a series of various organizational reforms in response to the Separatist threat, the charismatic Palpatine took control of the Senate. During the Clone Wars, Sate Pestage was in charge of the Senate's executive agenda.
During the time of the Empire, the Galactic Senate was known as the Imperial Senate. However, this Senate was largely powerless, with its members discouraged to disagreeing with the Emperor's wishes. Immediately before the Battle of Yavin, Palpatine officially dissolved the Imperial Senate. It was not until 6.5 ABY that the New Republic restored it, soon after liberating Coruscant.
The Senate was led by a Supreme Chancellor, elected by a vote of the Senate from amongst its delegates. He had little real authority over the Senate other than prerogative to call for a special session and could be removed by a vote of no confidence. The Vice Chair, also elected and removed by the Senate, wielded far more power being empowered to open, close and moderate debate on each motion, which allowed him to control agenda within the Senate.
The Galactic Senate was made up of over 2,000 congressmen: governor-delegates (referred to as senators) and representatives, representing sectors, systems, individual planets, or even Corporation or Guilds. Some were elected directly, while others were appointed by a planet's ruler (or even were the planet's ruler). Diplomats, religious figures, local political leaders, and other prominent people could also address the Senate as part of a senatorial delegation. Senators, however, were the only members with voting power, with the Representatives organized into the Galactic Representative Commission, although they could be appointed by their absent Senators as their temporary subsitute, and still could have a minor voice in Senate business.
Before the invasion of Naboo, Republic-member worlds could join or become signatories to various federations or groups. Often, smaller worlds would give their voting power over to these Federations in exchange for lucrative trade deals. This allowed various corporations, guilds, federations, and businesses to gain extra power in the Senate.
The Senate was divided into many committees and subcommittees, each to handle various issues of Galactic government and lawmaking. Some of them were:
In addition to the formal committees, there were informal political factions in the Senate as well. In the years leading up to the Battle of Naboo, there were two main ones: the Core faction and the Rim faction.
During the Clone Wars, the supermajority of the Senate supported Palpatine, allowing him to amend the Galactic Constitution and be granted more emergency powers.
The Senate was the legislative and executive power of the Republic (although at various times by the end of the Republic's existence, the Office of the Supreme Chancellor held supreme dictator Legislative, Executive, and Judicial authority). It also had limited judicial authority, presumably for high-profile plaintiffs or cases too controversial for (or tried in) the Supreme Court. Such cases included trying senators for treason (as wished by Vien'sai'Malloc); crimes against civilization (the interrupted trial of Ulic Qel-Droma); and presumably corruption and treason of the Supreme Chancellor (as Anakin Skywalker wished for Palpatine).
The following are documents passed by the Galactic Senate or relating to its functioning.
Thousands of years before the fall of the Republic, the Senate was housed in a hall building. At some point after the end of the Great Sith War, the Senate was relocated to the more advanced and spacious Senate Building.
The exterior portion of the Senate Building consisted of a large courtyard in front of the structure itself, a huge mushroom-shaped building.
The interior portion was a multiple-story room with thousands of chairs for senators from each world. In the center, the Supreme Chancellor would sit with his or her aides.
Although Episode I and Episode III refer to the Senate as "Congress," it is not actually one in the traditional sense of the word. A congress is usually an elected body that serves as the legislative branch (opposite an executive branch) in a presidential system. Because the Old Republic was a parliamentary system, the executive branch of the government was thusly derived from members of parliament in the legislative branch.
If anything, the direct threat to Senate sovereignty—Confederacy of Independent Systems (CIS)—is more of a "congress" than the Senate. The United States of America used the word "Congress" harkening back to the British colonies when delegates representing the east coast colonies first met to protest at their treatment by the government of Great Britain. They met as the "Continental Congress" which is somewhat similar to way that the CIS met regarding the way the corruption of the Senate, government, and Republic.
Moreover, unlike the traditional understanding of a parliament (or Congress, as it is referred), the Galactic Senate was a unicameral body (that is, it has one house), rather than the traditional bicameral body, which features both an upper house and a lower house. However, this would bring the Galactic Senate in line with the ancient Roman Senate, which was a unicameral body (even if the body was meant to be a merely advisory house, with little direct executive power).
Like many parliamentary systems, the executive branch (as aforementioned) would be elected by members within the Senate. The Supreme Chancellor serves as the prime minister, with the vice chair and speaker as deputies (though each have their own important functions within the structure of the Senate).
Furthermore, more evidence to suggest that the Galactic Senate is a parliamentary system (United Kingdom-style) as opposed to a congressional system (United States-style), as that there is no evidence of a "separation of powers" in the Galactic Senate—the executive, legislative, and judicial branches all seem to overlap, in a parliamentary system the executive is found within the legislative. Additionally, the Galactic Senate's system allows for a "vote of no confidence" to oust the current chancellor. No confidence votes are often found in parliamentary systems.
In background material composed by George Lucas in 1977 for licensees of the Expanded Universe, the "Republican Senate" represented a total of 24,372 systems and elected a Chancellor to a four year term. There was a term limit of one term. During a crisis, a Chancellor extended his term to 12 years and finally declared himself Emperor, first by rhetorically attacking the bureaucracy and then by aligning himself with it. The Jedi sided with the Senate after it attempted to impeach him. This story appears to be the germ of much of the events of the Prequel Trilogy.
The Galactic Senate represented the legislative branch of several forms of government. The Third Republic was one such example.