The Washington State Legislature is the state legislature of the State of Washington. It is a bicameral body, composed of the lower Washington House of Representatives, composed of 98 representatives, and the upper Washington State Senate, with 49 senators plus the lieutenant governor acting as president. The state is divided into 49 legislative districts, each of which elect one senator and two representatives.

The state legislature meets in the Legislative Building at the Washington State Capitol in Olympia.

As of January 2025, Democrats control both houses of the Washington State Legislature. Democrats hold a 59–39 majority in the House of Representatives and a 30–19 majority in the Senate.^{[unreliable source?]}

The Washington State Legislature traces its ancestry to the creation of the Washington Territory in 1853, following successful arguments from settlers north of the Columbia River to the U.S. federal government to legally separate from the Oregon Territory. The Washington Territorial Assembly, as the newly created area's bicameral legislature, convened the following year. The legislature represented settlers from the Strait of Juan de Fuca to modern Montana.

From nearly the start of the territory, arguments over giving women the right to vote dogged legislative proceedings. While some legislators carried genuine concerns over women deserving the right to vote, most legislators pragmatically believed that giving women suffrage would entice more Eastern women to immigrate to the remote and sparsely populated territory. In 1854, only six years after the Seneca Falls Convention, the issue was brought to a vote by the legislature. Women's suffrage was defeated in a tied vote of 9 to 9 (an absolute majority, or 10 votes, was needed to pass laws). This was due to one legislator voting against this bill because he had an American Indian wife and only white women would have been able to vote.

A decade later, the Wyoming Legislature would become the first body in the United States to grant women's suffrage in 1869.

The issue over female suffrage did not diminish. In 1871 Susan B. Anthony and Thurston County Representative Daniel Bigelow addressed the legislature on the issue. In 1883, the issue returned to the floor, this time with the Territorial Assembly successfully passing universal suffrage for women. It quickly became one of the most liberal voting laws in the nation, giving female African-American voters the voting franchise for the first time in the United States. However, in 1887, the territorial Washington Supreme Court ruled the 1883 universal suffrage act as unconstitutional in Harland v. Washington. Another attempt by the legislature to regrant universal female suffrage was again overturned in 1888.

After two failed voter referendums in 1889 and 1897, activism led by Emma Smith DeVoe and May Arkwright Hutton, among others, led the state legislature to approve the state constitutional amendment granting full female voting rights, which Washington's (male) voters ratified in 1910 by a vote of 52,299 to 29,676.