The legislature is an equal branch of the West Virginia government along with the executive and judicial departments, under the state constitution's separation of powers provision. The Senate’s 34 members serve four-year terms and represent 17 two-member districts. The terms are staggered, with one senator from each district elected every two years. The 100 members of the House of Delegates serve two-year terms in 100 single-member districts, with the entire membership elected at once; there were 56 districts, some with multiple members, before the state switched to single-member representation prior to the 2022 elections. Districts in each chamber are realigned following every federal census.

West Virginia's legislature originally had only 65 members, 18 senators and 47 delegates. The total grew to 89 in 1872 when the Senate membership was set at 24 and terms were increased from two to four years, and the House was fixed at 65 delegates and their terms expanded from one to two years. The current number of members was established for the House in 1952 and for the Senate in 1964.

Republicans held a decided numerical edge, particularly in the House, through the first six decades of the legislature's existence. In 1921, 99 of the 124 members were Republicans. Ten years later, Democrats had an 81-43 advantage, and when the party took control of the Senate 24-6 in 1933, it never lost the majority in either chamber through the remainder of the century. The most Republicans reelected from 1932 on totaled 43 in the House in 1972 and 12 in the Senate in 1968. In 1991, Donna Jean Boley of Pleasants County was the lone Republican among 34 senators. As few as nine Republicans were delegates following the 1964 and 1976 elections, reaching a maximum number of 43 in 1972. Democrats maintained a large majority in both houses until the 2014 election, when both bodies flipped to Republican. In subsequent elections, Republicans gained an increasingly larger majority. After the 2024 general elections, Republicans hold 91-9 advantage in the House and 32-to-2 advantage in the Senate.

The Senate had 15 members from each party after the 1910 and 1912 elections and the first such tie led to one of the most unusual events in legislative history. At the time, U.S. senators were appointed by the legislature. During the 1911 legislative session when the two parties deadlocked, Republican senators absented themselves from the state. They rode a train to Cincinnati where they stayed in a hotel and prevented the Senate from being able to meet in Charleston because of the lack of a quorum of 16 members. The tie was never broken, but a compromise was worked out whereby Republicans elected the Senate president and Democrats chose the U.S. senators. Much of the credit for the compromise is given to the clerk of the Senate at the time, John T. Harris of Parkersburg.

The legislature, required to convene at the seat of government, met in Wheeling from 1863 to 70, in Charleston the following five years, and again in Wheeling from 1875 until the capital was permanently moved back to Charleston in 1885. Members first convened in the present statehouse in 1932. The legislature met biennially between 1875 and the ratification in 1954 of a constitutional amendment providing for full two-month sessions one year, followed by a 30-day budget session the next year. Annual 60-day sessions were established by the Legislative Improvement Amendment, ratified in 1970.

Men have dominated the makeup of the legislature. Democrat Anna Johnson Gates became the first female member when she won one of Kanawha County's six House seats in 1920. Republican Minnie Buckingham Harper of McDowell County became the first Black woman to serve in a legislature in the United States when she was appointed in 1928 to the House seat left vacant by the death of her husband. Democrat Hazel Hyre of Jackson County became the first female senator in 1934 upon appointment to fill the unexpired term of her late husband. In 1966, Betty H. Baker, Hardy County Democrat, was the first woman elected to the Senate. Marshall University professor Marie E. Redd in 1998 became not only just the 18th female, but also the first African-American to be elected to the West Virginia Senate. There was a high total of 27 women legislators in 1989-90. As of 2024, the legislature had 16 women members (12 in the House, four in the Senate), marking the lowest rate of any state in the nation. In 2023, Delegate Sean Hornbuckle was elected minority leader for House Democrats, becoming the first Black person ever to hold that position in West Virginia.

Legislators are paid $20,000 annually, with additional compensation for travel, special sessions, and interim meetings. This is up from the $500 salary set by a constitutional amendment ratified in 1920 and the $1,500 approved by state voters in 1954. After proposed pay raises were rejected in the 1962 and 1966 statewide general elections, the constitution was amended in 1970 to provide for the creation of a citizens legislative compensation commission whose members were appointed by the governor. Lawmakers then could reduce but not increase levels of compensation and travel and expense reimbursement recommended by the seven-member commission.

Regular legislative sessions start on the second Wednesday of January of each year except every fourth year, when the session begins a month later to allow the incoming governor to prepare a state budget. Sessions may be extended by a concurrent resolution adopted by a two-thirds vote of the members elected to each house, or by proclamation of the governor for consideration of the budget only. Concurrent resolution by two-thirds may extend a session for budgetary as well as other legislative matters. The governor may call extraordinary sessions, and only items listed in the chief executive's proclamation may be considered. The legislature also has the authority to call itself into special session by a three-fifths petition, but since the agenda would be plenary or open-ended, the power has been rarely exercised.

Two annual sessions comprise a legislature, which begins in odd-number years following legislative elections the previous fall. Every legislature elects its officers to serve for the coming two sessions. The parties caucus beforehand, and majority-party nominees are virtually assured election by the full bodies during the opening organizational proceedings. The Senate elects a president and the House a speaker. The presiding officers each appoint floor leaders, committee chairs, and vice chairs and a pro tempore president and speaker, respectively. Each house also elects a clerk, sergeant-at-arms, and a doorkeeper, who are not members of the legislature.

Significantly, the Senate president and the House speaker are next in line to succeed as governor should that office become vacant during the chief executive's term. The two officers also possess broad legislative powers besides presiding during floor sessions. They may refer bills and resolutions to committee; control the corridors, passageways, and rooms assigned to each house; appoint committee members; sign acts of the legislature; designate office space; appoint members of conference committees on session matters of disagreement between the two houses and chair their respective rules committees. The two co-chair the legislature's Joint Committee on Government and Finance, which controls most legislative-related business, especially during interim meetings. The joint committee, with seven members from each house, was created in 1965 to study and survey matters of government, finance, and claims against the state and make recommendations to the full legislature. Its agencies include the commission on special investigations, court of claims, legislative auditor, rule-making review committee and divisions responsible for bill drafting, duplicating, technology, library services, research, and fiscal analysis.