1631

January–March

• January 23 - Thirty Years' War: Sweden and France sign the Treaty of Bärwalde, a military alliance in which France provides funds for the Swedish army invading northern Germany.
• February 5 - Puritan leader Roger Williams arrives in Boston.
• February 16 - The Reval Gymnasium is founded in Tallinn, Estonia, by Swedish king Gustavus II Adolphus.
• February 20 - A fire breaks out in Westminster Hall, but is put out before it can cause serious destruction.
• March 7 - Ambrósio I Nimi a Nkanga, the ruler of the Kingdom of Kongo dies after a reign of five years.
• March 10 - Al Walid ben Zidan becomes the new Sultan of Morocco upon the death of Abu Marwan Abd al-Malik II.
• March 20 - The siege of the Protestant German city of Magdeburg by the Catholic League begins and lasts for more than two months before the city falls and the inhabitants are massacred.

April–June

• April 13 - Thirty Years' War: Gustavus Adolphus of Sweden defeats an imperial garrison at the city of Frankfurt an der Oder.
• May 18 - In Dorchester, Boston, John Winthrop takes the oath of office, and becomes the first Governor of Massachusetts.
• May 20 - Thirty Years' War: After a two-month siege, the Imperial Army of the Holy Roman Emperor, under the command of Johann Tserclaes, Count of Tilly sacks the Protestant German city of Magdeburg, and massacres over 20,000 inhabitants. Shocked by the massacre, many Protestant states in the Holy Roman Empire decide to ally with Gustavus Adolphus of Sweden, and support his ongoing invasion.
• May 28 - William Claiborne sails from England to establish a trading post on Kent Island, the first English settlement in Maryland.
• May 30
• * Thirty Years' War: Bavaria and France sign the Treaty of Fontainebleau, forming a secret alliance; however, this does not last long.
• * Gazette de France, the first weekly French newspaper, is published.
• June 17 - The death in childbirth of Mumtaz Mahal at Burhanpur causes her husband Shah Jahan to commission the Taj Mahal at Agra, as a mausoleum for her. Construction is started in 1632, and finished in 1653.
• June 19 - War of the Mantuan Succession: The Treaty of Cherasco is signed, ending the War of the Mantuan Succession.
• June 20 - Algerian pirates sack Baltimore, County Cork, in Ireland.

July–September

• July 9 - Koca Musa Pasha, the Ottoman Governor of Egypt, arranges the murder of Emir Kitas Bey, commander of Turkish troops who had been scheduled to invade Persia.
• July 16 - The city of Würzburg is taken by Gustavus Adolphus of Sweden, putting an end to the Würzburg witch trials, but not before an estimated 900 people from the city and its environs have been burned at the stake for witchcraft.
• July 22 - Thirty Years' War - Battle of Werben: Tilly defeats Gustavus Adolphus of Sweden, but not decisively.
• August 22 - The Treaty of Werben is signed as an alliance between Hesse-Cassel and Sweden.
• August 29 - Abd Allah ibn Hasan, Emir of Mecca, abdicates in favor of two successors, his son Muhammad ibn Abd Allah and his great-nephew Zayd ibn Muhsin.
• August - Thirty Years' War: Running out of supplies, Tilly is forced to send his army into the Electorate of Saxony in order to secure supplies, as well as to force a reaction from John George, Elector of Saxony and Gustavus Adolphus of Sweden.
• September 11 - Thirty Years' War: As a result of Tilly's invasion, John George, Elector of Saxony, who has until now stayed neutral, allies with Gustavus Adolphus of Sweden, in order to drive the Imperial army out of Saxony.
• September 12 - Eighty Years' War - Battle of Albrolhos: A Spanish fleet, under the command of Admiral Antonio de Oquendo, defeats a Dutch fleet off the coast of Brazil.
• September 13- Eighty Years' War - Battle of the Slaak: A Spanish fleet of 95 ships, carrying 5,500 soldiers tasked with taking over the Dutch Republic, is almost completely destroyed the day after being intercepted by a Dutch fleet off of the coast of the Netherlands.
• September 17 - Thirty Years' War - Battle of Breitenfeld: Tilly's Holy Roman Imperial army is decisively defeated by Gustavus II Adolphus of Sweden, shattering the imperial army of the Holy Roman Empire, and marking the first significant victory for the Protestants in the war.

October–December

• October 10 - Thirty Years' War: A Saxon army takes over Prague.
• November 15 - King Gustavus Adolphus of Sweden takes possession of Prague, capital of Bohemia.
• November 21 - In Venice, a special mass celebrates the end of the two years of bubonic plague that had killed thousands of people.
• November 29 - The Treaty of Höchst is signed between King Gustavus Adolphus of Sweden and George II of Hesse-Darmstadt, with Darmstadt giving up the fortress of Rüsselsheim in return for Sweden's recognition of Darmstadt's neutrality.
• December 16 - A volcanic eruption of Mount Vesuvius at Pompeii occurs, for the first time in several centuries.
• December 23 - Thirty Years' War: Gustavus II Adolphus of Sweden takes the city of Mainz, without any resistance.

Date unknown

• Publication of
• * Moses Amyraut's Traite des Religions.
• * Chocolate: or, An Indian Drinke.