The 1918 United States Senate elections were held throughout 1918, the midpoint of Woodrow Wilson's second term as president. This was the first election since the ratification of the 17th Amendment that all 32 Class 2 senators were subject to direct or popular election, making them the final class under the old system of being selected by state legislatures. Special elections were also held to fill vacancies. Republicans gained a slim 2-seat control after picking a net of 6 seats up. This came after an April 1918 special election where they flipped a seat in Wisconsin.

Gains, losses, and holds

Retirements

Three Republicans and one Democrat retired instead of seeking re-election. Two Republicans retired instead of seeking election to finish the unexpired terms, one Democrat retired instead of seeking election to a full term and two Democrats retired instead of seeking election to finish the unexpired terms.

Defeats

Eight Democrats and one Republican sought re-election but lost in the primary or general election.

Deaths

One Democrat died on October 21, 1917, and his seat remained vacant until an April 1918 election.

Post-election changes

Source: United States Senate Official Website

Change in composition

Before the elections

Elections results

Complete list of races

Special elections during the 65th Congress

In these special elections, the winner was seated during 1918 or before March 4, 1919; ordered by election date.

Elections leading to the 66th Congress

In these general elections, the winners were elected for the term beginning March 4, 1919; ordered by state. All of the elections involved the Class 2 seats.

Closest races

Eighteen races had a margin of victory under 10%:

Alabama

Arkansas

Colorado

Delaware

Georgia

Idaho

Idaho (regular)

Idaho (special)

Incumbent Democratic Senator John Frost Nugent defeated Republican nominee Frank Robert Gooding by a very narrow margin of 1.00% and by 970 votes. Upon his election, John Frost Nugent became the first Democrat ever to have been elected to the United States Senate in Idaho or from Idaho and the first non-Republican to win a United States Senate seat in Idaho or from Idaho since 1901 and the first non-Republican to win the Class 3 Senate seat in Idaho or from Idaho since 1897.

Illinois

Iowa

Kansas

Kentucky

Louisiana

Louisiana (regular)

Louisiana (special)

Maine

Massachusetts

Michigan

Minnesota

Mississippi

Missouri (special)

Montana

Nebraska

Nevada (special)

New Hampshire

New Hampshire (regular)

New Hampshire (special)

New Jersey

New Jersey (regular)

New Jersey (special)

New Mexico

North Carolina

Oklahoma

Oregon

Oregon (regular)

Oregon (special)

Rhode Island

South Carolina

South Carolina (regular)

South Carolina (special)

South Dakota

Tennessee

Texas

Virginia

West Virginia

Wisconsin (special)

Wyoming