Events of 1845

January–June

• January 23 – The United State Congress establishes a uniform date for federal elections, which will henceforth be held on the first Tuesday after the first Monday in November.

• January 29 – The Raven by Edgar Allan Poe is published for the first time (New York Evening Mirror).

• February 1 – Anson Jones, President of the Republic of Texas, signs the charter officially creating Baylor University. Baylor is the oldest university in the State of Texas operating under its original name.

• February 7 – In the British Museum, a drunken visitor smashes the Portland Vase, which takes months to repair.

• February 28 – The United States Congress approves the annexation of Texas.

• March 1 – President John Tyler signs a bill authorizing the United States to annex the Republic of Texas.

• March 3 – Florida is admitted as the 27th U.S. state.

• March 4

• *The United States Congress passes legislation overriding a presidential veto for the first time.

• *James K. Polk succeeds John Tyler as President of the United States.

• March 11 – Flagstaff War: Chiefs Kawiti and Hone Heke lead 700 Māoris in the burning of the British colonial settlement of Kororareka (now known as Russell, New Zealand).

• March 13 – The Violin Concerto by Felix Mendelssohn premieres in Leipzig, with Ferdinand David as soloist.

• March 17 – The rubber band is invented in England.

• April – Ramón Castilla becomes the president of Peru.

• April 10 – A great fire destroys much of the city of Pittsburgh, Pennsylvania.

• May 20 – The HMS Erebus and Terror with 134 men under John Franklin sail from the River Thames, beginning a disastrous expedition to find the Northwest Passage.

July–December

• July 4 – Near Concord, Massachusetts, Henry David Thoreau embarks on a 2-year experiment in simple living at Walden Pond (see Walden).

• July 20 – Charles Sturt enters the Simpson Desert in central Australia.

• August 9 – The Aberdeen Act is signed.

• August 28 – The journal Scientific American begins publication.

• September 25 – The Phi Alpha Literary Society is founded.

• October 9 – The eminent and controversial Anglican, John Henry Newman, is received into the Roman Catholic Church.

• October 10 – In Annapolis, Maryland, the Naval School (later renamed the United States Naval Academy) opens with 50 midshipmen students and 7 professors.

• October 13 – A majority of voters in the Republic of Texas approve a proposed constitution, that if accepted by the United States Congress, will make Texas a U.S. state.

• October 21 – The New York Herald becomes the first newspaper to mention the game of baseball.

• October 22 – The New York Morning News becomes the first newspaper to include a box-score of a baseball game.

• November 20 – Battle of Vuelta de Obligado: The Argentine Confederation is narrowly defeated by an Anglo-French fleet on the waters of the Paraná River.

• December 2 – Manifest Destiny: U.S. President James K. Polk announces to Congress that the Monroe Doctrine should be strictly enforced and that the United States should aggressively expand into the West.

• December 5 – The Templars of Honor and Temperance is founded in the United States.

• December 6 – Alpha Sigma Phi Fraternity is founded.

• December 22–December 23 – Battle of Ferozeshah: British forces defeat Sikhs in Punjab.

• December 27 – Anesthesia is used for childbirth for the first time (Dr. Crawford Long in Jefferson, Georgia).

• December 27 - American journalist John L. Sullivan claims in a newspaper article that the United States have a "Manifest Destiny" to expand their borders. It's the second time he uses the term and it will have a huge influence on the American imperialistic movement of the 19th century.

• December 29 – Texas is admitted as the 28th U.S. state.

• December 30 – Queen's Colleges of Belfast, Cork, and Galway are incorporated in Ireland.

Undated

• The Republic of Yucatán separates for a second time from Mexico.

• Ephraim Bee reveals that the Emperor of China has given him a special dispensation; that he has entrusted him with certain sacred and mysterious rituals through Caleb Cushing, the U.S. Commissioner to China, to "extend the work and influence of the Ancient and Honorable Order of E Clampus Vitus" in the new world.

• In the United States Magazine and Democratic Review editor John L. O'Sullivan declares that foreign powers are trying to prevent American annexation of Texas in order to impede "the fullfillment of our manifest destiny to overspread the continent allotted by Providence for the free development of our yearly multiplying millions".

• Elizabeth Barret Browning writes the Sonnets from the Portuguese. 1845–1846.

• Frederick Douglass publishes his autobiography about slavery.

Ongoing events

• Great Irish Famine (1844–1849)

Births

• February 14 – Quintin Hogg, British philanthropist (d. 1903)

• February 15 – Elihu Root, American statesman and diplomat, recipient of the Nobel Peace Prize (d. 1937)

• February 25 – George Reid, fourth Prime Minister of Australia (d. 1918)

• March 3 – Georg Cantor, German mathematician (d. 1918)

• March 10 – Emperor Alexander III of Russia (d. 1894)

• March 20 – Victor Child Villiers, 7th Earl of Jersey, 18th Governor of New South Wales (d. 1915)

• March 27 – Wilhelm Conrad Röntgen, German physicist, Nobel Prize laureate (d. 1923)

• April 24 – Carl Spitteler, Swiss writer, Nobel Prize laureate (d. 1924)

• May 12 – Gabriel Fauré, French composer (d. 1924)

• May 16 – Ilya Ilyich Mechnikov, Russian microbiologist, recipient of the Nobel Prize in Physiology or Medicine (d. 1916)

• May 17 – Jacint Verdaguer, Catalan poet (d. 1902)

• May 25 – Eugène Grasset, Swiss-born artist (d. 1917)

• May 30 – King Amadeo I of Spain (d. 1890)

• June 7 – Leopold Auer, Hungarian violinist and composer (d. 1930)

• June 16 – Heinrich Dressel, German archaeologist (d. 1920)

• June 18 – Charles Louis Alphonse Laveran, French physician, recipient of the Nobel Prize in Physiology or Medicine (d. 1922)

• July 4 – Thomas John Barnardo, Irish philanthropist (d. 1905)

• July 18 – Tristan Corbière, French poet (d. 1875)

• July 19 – Horatio Nelson Young, American naval hero (d. 1913)

• August 10 – Abay Qunanbayuli, Kazakh poet (d. 1904)

• August 19 – Edmond James de Rothschild, French philanthropist (d. 1934)

• August 25 – King Ludwig II of Bavaria (d. 1886)

• October 21 – William McKendree Carleton, American poet (d. 1912) (pneumonia)

• November 3 – Edward Douglass White, 9th Chief Justice of the United States (d. 1921)

• November 4 – Vasudev Balwant Phadke, Indian revolutionary (d. 1883)

• November 10 – John Sparrow David Thompson, Prime Minister of Canada (d. 1894)

• December 9 – Joel Chandler Harris, American writer (d. 1908)

Deaths

• February 13 – Henrik Steffens, Norwegian philosopher (b. 1773)

• March 18 – Johnny Appleseed, pioneer (b. 1774)

• March 19 – Seku Amadu, founder of the Fula Massina Empire (b. 1773)

• April 10 – Dr. Thomas Sewall, American anatomist (b. 1786)

• May 12 – János Batsányi, Hungarian poet (b. 1763)

• May 15 – Braulio Carrillo Colina, Costa Rican Head of State (b. 1800)

• June 4 – Lasse-Maja, notorious Swedish criminal (b. 1785)

• June 8 – Andrew Jackson, 7th President of the United States (b. 1767)

• July 12

• *Friedrich Ludwig Persius, architect (b. 1803)

• *Henrik Wergeland, Norwegian writer (b. 1808)

• July 17 – Charles Grey, 2nd Earl Grey, Prime Minister of the United Kingdom (b. 1764)

• August 23 – Rafael Urdaneta, hero of the Latin American War of Independence (b. 1788)

• October 12 – Elizabeth Fry, British humanitarian (b. 1780)

• October 26 – Lady Nairne, Scottish songwriter (b. 1766)

• date unknown

• *Nicolás Espinoza, Head of State of El Salvador (b. 1795)