1865 is a common year starting on Sunday.
- January 31 - American Civil War: Confederate General Robert E. Lee becomes general-in-chief.
- February 17 - American Civil War: Columbia, South Carolina burns as Confederate forces flee from advancing Union forces.
- February 22 - Tennessee adopts a new constitution that abolishes slavery.
- March 3 - The United States Congress authorizes formation of the Freedmen's Bureau
- March 13 - American Civil War: The Confederate States of America reluctantly agrees to the use of African American troops.
- March 18 - American Civil War: The Congress of the Confederate States of America adjourns for the last time
- March 19 - American Civil War: The Battle of Bentonville begins. By the end of the battle on the 21st the Confederate forces had retreated from Greenville, North Carolina.
- March 25 - American Civil War: In Virginia, Confederate forces capture Fort Stedman from the Union.
- March 29 - American Civil War: Battle of Appomattox Court House begins
- April 1 - American Civil War: Battle of Five Forks - In Petersburg, Virginia, Confederate General Robert E. Lee begins his final offensive.
- April 2 - American Civil War: Confederate President Jefferson Davis and most of his Cabinet flee the Confederate capital of Richmond, Virginia which is taken the next day.
- April 6 - German Chemicals producer, Badische Anilin- und Sodafabrik(BASF) founded in Mannheim.
- April 9 - American Civil War: General Robert E. Lee surrenders to Ulysses S. Grant at Appomattox, effectively ending the American Civil War.
- April 14 - US President Abraham Lincoln is assassinated by John Wilkes Booth.
- April 21 - German Chemicals producer BASF moves its headquarters and factories from Mannheim to the Hemshof district of Ludwigshafen.
- April 26 - Union cavalry corner John Wilkes Booth and cavalryman Boston Corbett shoots the assassin dead.
- April 26 - American Civil War: Confederate General Joseph Johnston surrenders his army to General William Tecumseh Sherman at Durham Station, North Carolina.
- April 27 - The steamboat Sultana, carrying 2,300 passengers, explodes and sinks in the Mississippi River, killing 1,700, most of whom were Union survivors of the Andersonville Prison.
- May 1 - Triple Alliance of Argentina, Brazil and Uruguay against Paraguay is formally signed - War of the Triple Alliance is already going
- May 10 - American Civil War: Jefferson Davis is captured by Union troops near Irwinville, Georgia.
- May 13 - American Civil War: Battle of Palmito Ranch - In far south Texas, more than a month after Confederate General Lee's surrender, the last land battle of the civil war ends with a Union victory.
- May 23 - Parade down Pennsylvania Ave in Washington, DC to celebrate the ending of the American Civil War.
- May 25 - Mobile magazine explosion: 300 are killed in Mobile, Alabama when an ordnance depot explodes.
- June 2 - American Civil War ends - Forces under Confederate General Edmund Kirby Smith surrender at Galveston, Texas, becoming the last to do so.
- June 11 - Brazilian navy squadron defeats Paraguayn navy at Riachualo
- June 23 - American Civil War: At Fort Towson in Oklahoma Territory Confederate General Stand Watie surrenders the last significant rebel army.
- July 2 - Salvation Army founded in Whitechapel, London
- July 5 - William Booth founds the Christian Mission (later renamed to the Salvation Army).
- July 21 - In the market square of Springfield, Missouri, Wild Bill Hickok shoots Dave Tutt dead in what is regarded as the first true western showdown.
- July 27 - Welsh settlers arrive in Argentina at Chubut Valley.
- December 24 - Several US Civil War Confederate veterans form the Ku Klux Klan.
- January 5 - Julio Garavito Armero, Colombian astronomer (d. 1920)
- February 12 - Kazimierz Tetmajer, full name Kazimierz Przerwa-Tetmajer, Polish poet and writer (d. 1940)
- February 19 - Sven Hedin, scientist and explorer (+ 1952)
- March 15 - Edith Maude Eaton, writer (+ 1914)
- March 19 - William Morton Wheeler, american entomologist and ethologist
- May 25 - Pieter Zeeman, Nobel Prize winner (+ 1943)
- May 26 - Robert W. Chambers, artist (+ 1933)
- June 3 - King George V of the United Kingdom
- June 9 - Albéric Magnard, composer
- August 24 - King Ferdinand of Romania
- August 27 - James Henry Breasted, Egyptologist (d. 1935)
- October 1 - Paul Dukas, French composer
- October 26 - Benjamin Guggenheim, businessman, went down on Titanic
- December 8 - Jean Sibelius, composer
- April 1 - John Milton, governor of Florida
- April 2 - A.P. Hill, Confederate general
- April 15 - Abraham Lincoln, US President (b. 1809)
- April 26 - John Wilkes Booth, actor and assassin of Abraham Lincoln
- October 18 - Lord Palmerston, Prime Minister of Britain
- November 12 - Elizabeth Gaskell, British novelist, biographer
- November 28 - William Machin Stairs, Nova Scotia businessman, statesman
- December 10 - Leopold I of Belgium.
- James Barry, British military surgeon