The Constitution of the State of Wisconsin is the governing document of the U.S. State of Wisconsin. It establishes the structure and function of state government, describes the state boundaries, and declares the rights of state citizens. The Wisconsin Constitution was written at a constitutional convention held in Madison, Wisconsin, in December 1847 and approved by the citizens of Wisconsin Territory in a referendum held in March 1848. Wisconsin was admitted to the United States on May 29, 1848. Although it has been amended over a hundred times, the original constitution ratified in 1848 is still in use. This makes the Wisconsin Constitution the oldest U.S. state constitution outside New England; only Massachusetts, Maine, New Hampshire, and Vermont use older constitutions.

The Wisconsin Constitution contains a brief preamble and fourteen articles detailing the state government, its powers, and its limitations.

Although Wisconsin continues to use the original constitution ratified as Wisconsin achieved statehood, the current constitution is the second document to be proposed as the state constitution. In 1846, the residents of Wisconsin Territory first voted to apply for statehood, and they elected 124 representatives to meet in Madison to author a state constitution. These delegates, most of them elected as Democrats, met in the fall of 1846 to write the constitution. But the document they produced by December 1846 contained several provisions which were deemed radical at the time. The document gave married women the right to own property and allowed for a public referendum to settle the issue of African American suffrage. In addition, Edward G. Ryan, the delegate from Racine, Wisconsin, introduced a section to the constitution that prohibited all commercial banking in Wisconsin. Not ready to accept some of these provisions, the public rejected the first proposed constitution in a referendum and elected a second delegation to write a constitution which would be more acceptable to the people.

The second constitutional convention produced a much more conservative document that lacked the controversial progressive clauses in its predecessor. The second draft constitution was mute on the controversial issues of women's property rights. It gave suffrage only to white male citizens over the age of twenty one and American Indians that had been made citizens of the United States, but gave the legislature the ability to extend suffrage to other groups through laws approved by public referendum. Although drafted in English, the drafters contracted with publishers of newspapers in the territory, not printed in the English language, to translate the constitution into the languages in which such newspapers were printed. The issue of banking was put to a public vote; citizens could decide for themselves whether or not the state legislature could pass laws allowing banking after the constitution was ratified. The second proposed constitution was finished in December 1847, and was approved by the public in March 1848. During the same election, voters also chose to allow the legislature to charter banks. Shortly after the referendum, the state constitution was ratified by the United States Senate and put into effect with the election of the first state officials.

The Constitution begins with the following preamble:

We, the people of Wisconsin, grateful to Almighty God for our freedom, to secure its blessings, form a more perfect government, insure domestic tranquility and promote the general welfare, do establish this constitution.

— Wisconsin Constitution, preamble

The first article of the Wisconsin constitution outlines the legal rights of state citizens. In addition to reaffirming the rights guaranteed in the United States Bill of Rights, Article I of the Wisconsin Constitution offers additional guarantees to its citizens. Among these are sections which prohibit slavery, prohibit imprisonment for debt, guarantee resident aliens the same property rights as citizens, affirm that the military is subordinate to civil authorities, allow for the use of state owned school buildings by civil and religious organizations during non-school hours, and guarantee the right of citizens to hunt and fish.