The Michigan Senate is the upper house of the Michigan Legislature. Along with the Michigan House of Representatives, it composes the state legislature, which has powers, roles and duties defined by Article IV of the Michigan Constitution, adopted in 1963. The primary purpose of the Legislature is to enact new laws and amend or repeal existing laws.

The Michigan Senate is composed of 38 members, each elected from a single-member district with a population of between approximately 212,400 to 263,500 residents. Legislative districts are drawn on the basis of population figures, provided by the federal decennial census. In January 2023, Democrats took the majority with 20 seats to Republicans' 18 seats. The Senate chamber is located in the State Capitol building.

Members of the Michigan Senate are called senators. Because this shadows the terminology used to describe members of the United States Senate, constituents and the news media, using The Associated Press Stylebook, often refer to members of the Michigan Senate as state senators when necessary to avoid confusion with their federal counterparts.

Senators are elected on a partisan basis for four-year terms, concurrent with the election of the Governor of Michigan. Terms for senators begin on January 1 at noon, following the November general election and end on January 1 when their replacements are sworn in.

Senate elections are always held two years after the election for President of the United States, with the next election scheduled for November 3, 2026.

On November 3, 1992, almost 59 percent of Michigan voters backed Proposal B, the Michigan Term Limits Amendment, which amended the state constitution, to enact term limits on federal and state officials. In 1995, the U.S. Supreme Court ruled that states could not enact congressional term limits, but ruled that the state-level term limits remain. Under the amendment, a person could be elected to the state senate two times. A provision governing partial terms was also included. These provisions became Article IV, section 54 and Article V, section 30 of the Michigan Constitution. On November 8, 2022, nearly 2 in 3 voters approved Proposal 1, limiting state legislators to 12 years combined in either chamber of the legislature, but incumbent senators re-elected in 2022 would remain eligible for their new terms even if it pushed them over the 12-year limit and newly elected senators would similarly be eligible for a second term in 2026 regardless of previous legislative service.

Each senator must be a citizen of the United States, at least 21 years of age, and an elector of the district they represent. Under state law, moving out of the district shall be deemed a vacation of the office. No person who has been convicted of subversion or who has within the preceding 20 years been convicted of a felony involving a breach of public trust shall be eligible for either house of the legislature.

For reckoning periods of time during which the legislature operates, each two-year period coinciding with the election of new members of the House of Representatives is numbered consecutively as a legislature, dating to the first legislature following Michigan's admission as a state. The current two-year term of the legislature (January 1, 2025 – December 31, 2026) is the 103rd Legislature.