The New Jersey Senate is the upper house of the New Jersey Legislature by the Constitution of 1844, replacing the Legislative Council. There are 40 legislative districts, representing districts with an average population of 232,225 (2020 figure). Each district has one senator and two members of the New Jersey General Assembly, the lower house of the legislature. Prior to the election in which they are chosen, senators must be a minimum of 30 years old and a resident of the state for four years to be eligible to serve in office.

From 1844 until 1965 (when the Reynolds v. Sims US Supreme Court decision mandated all state legislators be elected from districts of roughly equal population), each county was an electoral district electing one senator. Under the 1844 Constitution, the term of office was three years, which was changed to four years with the 1947 Constitution. Since 1968 the Senate has consisted of 40 senators, who are elected in a "2-4-4" cycle. Senators serve a two-year term at the beginning of each decade, with the rest of the decade divided into two four-year terms. The "2-4-4" cycle was put into place so that Senate elections can reflect the changes made to the district boundaries on the basis of the decennial United States Census. If the cycle were not put into place, then the boundaries would sometimes be four years out of date before being used for Senate elections. Rather, with the varied term, the boundaries are only two years out of date. Thus elections for Senate seats take place in years ending with a "1", "3", or "7" (i.e. next elections in 2023, 2027, and 2031).

New Jersey Senate

Interim appointments are made to fill vacant legislative seats by the county committee or committees of the party of the vacating person (since a constitutional amendment passed on November 8, 1988). The office is on the ballot for the next general election, even if the other Senate seats are not up for election in that year (such as in years ending with a "5" or "9", such as 2009 or 2015). The sole exception to this is if the vacancy occurred within 51 days of the election, in which case the appointment stands until the following general election.

New Jersey Senate

"Double dipping" Under a state law that remained in effect until 2008, members of the New Jersey Assembly and Senate were allowed to serve in either chamber, as well as any other government positions they might have held at the time, although those who were still doing so as of 2008 ended up getting "grandfathered":

New Jersey Senate

Name, Party-County – Second Public Office (names in bold represent state Senators still in both local and state offices as of 2023):

Senators: Dana Redd, D-Camden – Councilwoman, Camden Nicholas Sacco, D-Hudson – Mayor, North Bergen Paul Sarlo, D-Bergen – Mayor, Wood-Ridge Robert Singer, R-Ocean – Committeeman, Lakewood Brian Stack, D-Hudson – Mayor, Union City Stephen Sweeney, D-Gloucester – Freeholder, Gloucester County

Senatorial courtesy

Senatorial courtesy is a senate tradition that allows home county legislators to intercede to prevent consideration of a local resident nominated by the governor for a position that requires Senate confirmation. Any of the senators from the nominee's home county can invoke senatorial courtesy to block a nomination, temporarily or permanently, without any obligation to justify the basis of their actions.

Governor Corzine nominated Stuart Rabner on June 4, 2007, to be the next Chief Justice of the New Jersey Supreme Court, replacing James R. Zazzali, who was nearing mandatory retirement age. Shortly after the nomination, two members of the Senate from Essex County, where Rabner resides, blocked consideration of his confirmation by invoking senatorial courtesy. State Senator Ronald Rice had initially blocked the nomination, but relented on June 15, 2007, after a meeting with the governor. Nia Gill dropped her block on June 19, 2007, but did not explain the nature of her concerns, though anonymous lawmakers cited in The New York Times indicated that the objection was due to Rabner's race and Governor Corzine's failure to consider a minority candidate for the post.

Also in June 2007, Loretta Weinberg used senatorial courtesy privileges to hold up consideration of a new term in office for Bergen County Prosecutor John Molinelli.

Acting governor

Until 2010, in the event of a gubernatorial vacancy, the New Jersey Constitution had specified that the President of the Senate (followed by the Speaker of the New Jersey General Assembly) would assume the role of Acting Governor and retain their role in the Senate (or Assembly). An Acting Governor would then assume the governorship while retaining their role in their house of the legislature.