Monarch: Leopold I (until 10 December); Leopold II (from in 17 December)

Head of government: Charles Rogier

March

• 16 March – Belgian state guarantees private savings.^[1]: 679

April

• 4 April – Opposition parties accuse government of breaching Belgian neutrality by involving the country in the Second French intervention in Mexico.^[1]: 678

May

• 1 May – Henricus Franciscus Bracq consecrated as bishop of Ghent
• 22 May — Commercial treaty with the German Customs Union signed in Berlin.^{[2]: 177–197}
• 26 May – 1863–75 cholera pandemic caused 45,000 fatalities in Belgium in 1865.^[1]: 678

July

• 16 July – Belgian Legion wins Battle of la Loma in Mexico.^[1]: 679

August

• 21 August — Law on tariffs and customs reform published.^[2]: i-v

September

• 23 September – Brussels city council approves plans for the covering of the Senne.^[1]: 680

October

• 2 October – Sint-Lievenscollege founded in Ghent

November

• 2 November – Treaty of Amity, Commerce and Navigation between China and Belgium, negotiated by Auguste t'Kint, signed in Beijing.^[3]
• 14 November – Jules Bara succeeds Victor Tesch as Minister of Justice.^[1]: 680

December

• 10 December – Death of King Leopold I of Belgium.
• 16 December – Leopold I of Belgium buried in Laken, despite his wish to be buried in Windsor;^[1]: 681 Auguste t'Kint arrives in Yokohama as the first Belgian diplomat in Japan.^[3]
• 17 December – Leopold II of Belgium sworn in as King.
• 23 December — Convention between France, Belgium, Italy and Switzerland forming the Latin Monetary Union signed in Paris.^{[2]: 240-308}

Periodicals

• Almanach royal officiel (Brussels, H. Tarlier and Rozez)^[4]
• Analectes pour servir à l'histoire ecclésiastique de la Belgique, vol. 2, edited by P. F. X. de Ram.^[5]
• Annales de la Société d'émulation pour l'étude de l'histoire et des antiquités de la Flandre, 2nd series, vol. 13 (Bruges, Vandecasteele-Werbrouck)^[6]
• Annuaire de l'Université catholique de Louvain, vol. 29 (Leuven, Vanlinthout)^[7]
• Collection de précis historiques, vol. 14, edited by Edouard Terwecoren S.J.^[8]
• La Liberté begins publication (March).^[1]: 679
• Revue Générale begins publication (January).^[1]: 678
• Rond den Heerd begins publication (December).^[1]: 680

Scholarship

• Émile de Borchgrave, Histoire des colonies belges, qui s'établirent en Allemagne pendant le XIIe et le XIIIe siècle (Brussels)
• Joseph Jean De Smet (ed.), Recueil des chroniques de Flandre, vol. 4 (Brussels, Commission royale d'Histoire)^[9]
• Joseph Jean De Smet, Mémoire historique sur la guerre de Maximilien, roi des Romains, contre les villes de Flandre (1482-1488) (Brussels, Hayez for Royal Academy of Science, Letters and Fine Arts of Belgium) – a study of the Flemish revolts against Maximilian of Austria.^[10]
• Paul Henrard, Histoire de l'artillerie en Belgique depuis son origine jusqu'au règne d'Albert et d'Isabelle (Brussels, C. Muquardt)^[11]
• Alphonse O'Kelly de Galway, Dictionnaire des cris d'armes et devises des personnages célèbres et des familles nobles et autres de la Belgique ancienne et moderne (Brussels, A. Schnée)^[12]

Literature

• Hendrik Conscience, De Burgemeester van Luik

Buildings

• Arlon Synagogue completed.

Paintings

• Henri Leys, Lucie Leys

• Louis Melsens receives Montyon Prize for his work on the use of potassium iodide to treat mercury poisoning and lead poisoning.^[1]: 678

In 1865 imports to Belgium were valued at 1.364 million francs, with exports of 1.204 million francs.^[13]

• Date uncertain – Joseph Middeleer, painter (died 1939)
• 19 January – Égide Rombaux, sculptor (died 1942)
• 27 January – Ferdinand Feyerick, fencer (died 1920)
• 30 January – Marie de Bièvre, painter (died 1909)
• 25 February – Flavie Van den Hende, cellist (died 1925)
• 2 March – Théo Ysaÿe, composer (died 1918)
• 7 March – Jean Massart, botanist (died 1925)
• 2 April – Louise Danse, painter (died 1948)
• 4 April – Clément Van Bogaert, engineer (died 1937)
• 1 May – Frans Mortelmans, painter (died 1936)
• 4 May – Servais Le Roy, entertainer (died 1953)
• 9 May – August de Boeck, composer (died 1937)
• 21 May – Evert Larock, painter (died 1901)
• 6 June – Antoon Jozef Witteryck, publisher (died 1934)
• 15 June – Paul Gilson, composer (died 1942)
• 14 July – Marguerite Verboeckhoven, painter (died 1949)
• 11 December – Édouard Poncelet, archivist (died 1947)

• 3 January – Joseph Lies, painter (born 1821)
• 5 January – Pierre Kersten, publisher (born 1789)
• 14 January – Marie-Anne Libert, botanist (born 1782)
• 19 March – Joseph Lebeau, politician (born 1794)
• 26 April – Charles-Joseph Sax musical instrument maker (born 1790)
• 14 May – Pierre François Xavier de Ram, historian (born 1804)
• 18 June – Antoine Wiertz, painter (born 1806)
• 12 July – Constant de Kerchove de Denterghem, politician (born 1790)
• 23 July – Frans Alfons Janssens, priest-scientist (died 1924)