The methods for filling vacancies in the U.S. Congress vary greatly, and for good reason, between the Senate and the House of Representatives.

When a U.S. representative or senator leave Congress before the end of his or her term, are the people of their congressional district or state left without representation in Washington?

Key Takeaways: Vacancies in Congress Vacancies in the U.S. Congress occur when a senator or representative dies, resigns, retires, is expelled, or is elected to another office before the end of their regular term.

Most vacancies in the Senate can be filled immediately through an appointment made by the governor to the former senator’s state.

Vacancies in the House can take as long as six months to fill, because representatives can only be replaced through a special election.

Members of Congress; senators, and representatives, usually leave office before the end of their terms for one of five reasons: death, resignation, retirement, expulsion, and election or appointment to other government posts.

Vacancies in the Senate

The chamber of the United States Senate. Wally McNamee/Getty Images

While the U.S. Constitution does not mandate a method by which vacancies in the Senate are to be handled, vacancies can be filled almost immediately through an appointment made by the governor of the former senator's state. The laws of some states require the governor to call a special election to replace U.S. senators. In states where replacements are appointed by the governor, the governor almost always appoints a member of his or her own political party. In some cases, the governor will appoint one of the state's current U.S. representatives in the House to fill the vacant Senate seat, thus creating a vacancy in the House. Vacancies in Congress also occur when a member runs for and is elected to some other political office before his or her term is over.

In 36 states, the governors appoint temporary replacements for vacant Senate seats. At the next regularly scheduled election, a special election is held to replace the temporary appointees, who may run for the office themselves.

In the remaining 14 states, a special election is held by a specified date to fill the vacancy. Of those 14 states, 10 allow the governor the option of making an interim appointment to fill the seat until the special election is held.

Since Senate vacancies can be filled so quickly and each state has two senators, it is highly unlikely that a state would ever be without representation in the Senate.

The 17th Amendment and Senate Vacancies

Until ratification of the 17th Amendment to the U.S. Constitution in 1913, vacant seats in the Senate in the same way Senators themselves were chosen — by the states, rather than by the people.

As originally ratified, the Constitution specified that Senators were to be appointed by the legislatures of the states rather than elected by the people. Similarly, the original Constitution left the duty of filling vacant Senate seats solely to the state legislatures. The framers felt that granting the states the power to appoint and replace senators would make them more loyal to the federal government and increase the new Constitution’s chances of ratification.

However, when repeated lengthy Senate vacancies began to delay the legislative process, the House and Senate finally agreed to send the 17th Amendment requiring the direct election of senators to the states for ratification. The Amendment also established the current method of filling Senate vacancies through special elections.

Vacancies in the House

The U.S. House of Representatives chamber is seen December 8, 2008 in Washington, DC. Brendan Hoffman/Getty Images

Vacancies in the House of Representatives typically take far longer to fill. The Constitution requires that member of the House be replaced only by an election held in the congressional district of the former representative.

"When vacancies happen in the Representation from any State, the Executive Authority thereof shall issue Writs of Election to fill such Vacancies." -- Article I, Section 2, Clause 4 of the U.S. Constitution

During the first two-year session of a Congress, all states, territories, and the District of Columbia are required by current federal law to hold special elections to fill any vacant House seat. However, during the second session of a Congress, procedures often vary depending on the amount of time between the date the vacancy occurs and the date of the next general election. For example, under Section 8 of Title 2, United States Code, a state’s governor can hold a special election at any time in extraordinary circumstances, such as a crisis resulting in the number of vacancies in the House exceeding 100 of the 435 seats.

According to the U.S. Constitution and state law, the governor of the state calls for a special election to replace the vacant House seat. The full election cycle must be followed including political party nominating processes, primary elections and a general election, all held in the congressional district involved. The entire process often takes as long as from three to six months.

While a House seat is vacant, the office of the former representative remains open, its staff operating under the supervision of the Clerk of the House of Representatives. The people of the affected congressional district do not have voting representation in the House during the vacancy period. They can, however, continue to contact former representative's interim office for assistance with a limited range of services as listed below by the Clerk of the House.\

Join session of the United States congress meets in 1915. Harris & Ewing/Wikimedia Commons/Public Domain

Legislative Information from Vacant Offices

Until a new representative is elected, the vacant congressional office cannot take or advocate positions of public policy. Constituents may choose to express opinions on legislation or issues to your elected Senators or wait until a new representative is elected. Mail received by the vacant office will be acknowledged. The staff of the vacant office can assist constituents with general information concerning the status of legislation, but cannot provide analysis of issues or render opinions.

Assistance With Federal Government Agencies

The staff of the vacant office will continue to assist constituents who have cases pending with the office. These constituents will receive a letter from the Clerk requesting whether the staff should continue assistance or not. Constituents who do not have pending cases but require assistance in matters relating to federal government agencies are invited to contact the nearest district office for further information and assistance.