The 1999 United States state legislative elections were held on November 2, 1999, alongside other elections. Elections were held for 7 legislative chambers in four states. Both chambers of the Northern Mariana Islands legislature were up.
Democrats maintained control of the Mississippi and Louisiana legislatures, while Republicans maintained control of the lower house in New Jersey and the upper house in Virginia. Republicans had won a 1997 special election to claim a 21-19 majority in the Virginia Senate after Democrat Charles L. Waddell resigned his seat. Republicans maintained this majority in 1999, which gave them their first-ever elected majority in history. Republicans flipped the Virginia House of Delegates, which was previously tied, resulting in the first-ever Republican majority.
Additionally, in the summer of 1999, a Democratic senator died in the New Hampshire Senate and was succeeded by a Republican in a special election, switching that chamber from Democratic control to tied.
Regularly scheduled elections were held in 7 of the 99 state legislative chambers in the United States. Nationwide, regularly scheduled elections were held for 538 of the 7,383 legislative seats. This table only covers regularly scheduled elections; additional special elections took place concurrently with these regularly scheduled elections.
All seats of the Louisiana State Senate and the Louisiana House of Representatives were up for election to four-year terms in single-member districts. Democrats maintained control of both chambers.
All seats of the Mississippi State Senate and the Mississippi House of Representatives were up for election to four-year terms in single-member districts. Democrats maintained control of both houses.
All seats of the New Jersey General Assembly were up for election. Assembly members were elected to two-year terms in two-member districts. Republicans retained control.
All seats of the Senate of Virginia and the Virginia House of Delegates were up for election in single-member districts. Senators were elected to four-year terms, while delegates served terms of two years. Republicans maintained control of the Senate and flipped the House of Delegates, which was previously tied.
All seats of the Northern Mariana Islands House of Representatives and half of the Northern Mariana Islands Senate are up for election. Senators are elected to four-year terms, and Representatives are elected to two-year terms. Republicans maintained control of both houses.