1544

January–June

• January 13 - At Västerås, the estates of Sweden swear loyalty to King Gustav Vasa and to his heirs, ending the traditional electoral monarchy in Sweden. Gustav subsequently signs an alliance with the Kingdom of France.
• February 20 - The Fourth Diet of Speyer is convened.
• April 11 - Battle of Ceresole: French forces under the Comte d'Enghien defeat forces of the Holy Roman Empire, under the Marques Del Vasto, near Turin.
• May - Charles V, Holy Roman Emperor, again invades eastern France.
• May 3 - Edward Seymour, Earl of Hertford, with an English army, captures Leith and Edinburgh from the Kingdom of Scotland.
• June 19-August 18 - Troops of the Holy Roman Empire besiege Saint-Dizier, in eastern France.

  July–December

• July - Battle of the Shirts: The Clan Fraser of Lovat and Macdonalds of Clan Ranald fight over a disputed chiefship in Scotland; reportedly, five Frasers and eight Macdonalds survive.
• July 19-September 14 - Italian War of 1542–46 - First Siege of Boulogne: King Henry VIII of England besieges and captures Boulogne in northern France.
• August 17 - The University of Königsberg is inaugurated.
• September 18 - Peace of Crépy: Peace is declared between Charles V, Holy Roman Emperor, and Francis I of France. The war between France and England continues.
• September 22 - Captain Juan Bautista Pastene leads the first European expedition to the estuary of Valdivia, Chile and Corral Bay.
• October 9 - Second Siege of Boulogne: French forces under the Dauphin assault Boulogne, but are ultimately unsuccessful.

  Date unknown

• Mongols burn the suburbs of Peking in China.
• The Orto botanico di Pisa botanical garden is established by Cosimo I de' Medici, Grand Duke of Tuscany, in Italy, under the direction of botanist Luca Ghini, who also creates the first herbarium.
• Rats make their first appearance in North America.
• Portuguese explorers encounter the island of Taiwan, and call it Ilha Formosa.