Johan de Witt (September 24, 1625 - August 20, 1672) was a significant Dutch political figure.

He studied at the University of Leiden where he excelled at mathematics and law. He received his doctorate from the University of Angers in 1645. He practiced law as an attorney in The Hague as an associate with the firm of Frans van Schooten

In 1650 he was appointed leader of the deputation of Dordrecht to the government of Holland. He became the leader of this government in 1653. As leader of Holland he applied his mathematical knowledge to the republic's financial and budgetary problems.

Johan de Witt brought about peace with England after the First Anglo-Dutch War with the Treaty of Westminster in the year 1654. For the next thirteen years the republic increased in wealth and influence under his leadership. The Second Anglo-Dutch War began in 1665, lasting until 1667 when it ended with the Treaty of Breda, in which Johan de Witt negotiated very favorable agreements for the republic.

In the Dutch rampjaar (disaster year) of 1672 he was assassinated by an angry mob after visiting his brother Cornelis de Witt in prison.