The following events occurred in July 1903:

• The first Tour de France bicycle race, sponsored by the French newspaper L'Auto in an effort to boost sales, is launched from the Café au Réveil-Matin in Paris.^[1]
• The metre gauge section of the Rhaetian Railway (RhB) in Switzerland opens, passing through the 1370 metre high Albula Tunnel in the Alps.^[2]
• The 1903 Wimbledon Championships draws to a close, with Laurence Doherty emerging as Men's Singles champion and Dorothea Douglass as Ladies' Singles champion.^[3]
• Raymond, Alberta, is incorporated as a town in Canada's North-West Territories.^[4]
• Born: Amy Johnson, English aviator, in Hull (died 1941)

• Under the Cuban–American Treaty of Relations, signed in May 1903, a second lease on Guantánamo Bay is signed by the U.S. and Cuba, as a result of which the U.S. will send a payment to the Cuban government each year in return for permission to use the land as a coaling and naval station.^[5]
• The 1903 Gordon Bennett Cup motor race is held at the Athy Circuit in Ireland and is won by Camille Jenatzy of Belgium.^[6]
• Born: Alec Douglas-Home, British politician, Prime Minister of the United Kingdom 1963–64, in London (died 1995); King Olav V of Norway, at Sandringham, UK (d. 1991)^[7]

• Born: Ace Bailey, Canadian ice hockey player, in Bracebridge, Ontario (died 1992)
• Died: Harriet Lane, 73, First Lady of the United States during the presidency of her uncle, James Buchanan

• Inaugural World Light Heavyweight Boxing Champion Jack Root loses his title, by a technical knockout, to George Gardiner at Fort Erie, Ontario, Canada, less than three months after winning it.^[8]

• Born: Hugo Theorell, Swedish scientist and Nobel laureate, in Linköping (died 1982)^[9]

• Born: O. E. Hasse, German film actor and director, in Obersitzko (died 1978)

• Born: Kenneth Clark, English art historian and broadcaster, in London (died 1983)

• Born: Adalberto Libera, Italian Modernist architect, in Trentino (died 1963)

• Died: James McNeill Whistler, 69, US painter

• US paddle steamer North Pacific loses its course in foggy conditions, strikes a rock off Marrowstone Island, Washington state, and sinks.

• The inaugural Tour de France is won by pre-race favourite, France's Maurice Garin.^[10]
• King Edward VII of the United Kingdom makes his first visit to Ireland since becoming king in 1901.^[11]

• Died: Pope Leo XIII, 93, Italian prelate (born Vincenzo Gioacchino Raffaele Luigi Pecci)

• The first tropical cyclone of the Atlantic hurricane season develops northeast of the Samaná Peninsula of Dominican Republic.

• The first Ford Model A automobile is sold to Chicago dentist Ernest Pfennig.^[12]

• In the by-election at Barnard Castle in the UK, brought about by the death of sitting Liberal MP, Sir Joseph Pease, Arthur Henderson takes the seat for Labour, becoming the first Labour candidate to win against both Liberal and Conservative opposition, and only the fifth Labour MP in the House of Commons.^[13]

• The weekly magazine Truth is launched in Perth, Western Australia, under the editorship of John Norton.^[14][15]

• Argentina's soccer champions, Alumni Athletic Club, lose their first match in four years, and the only one of the season, to Belgrano AC.^[16]

• Glasgow St Enoch rail accident: A Glasgow and South Western Railway train collides with buffer stops at St Enoch railway station, resulting in 17 deaths.^[17]
• Construction work begins on the Baghdad Railway in present-day Turkey.^[18]
• Born: Michail Stasinopoulos, Greek politician, President 1974–75, in Kalamata (died 2002)

• Idaho Springs miners' strike of 1903: Philip Fire, a striking union miner, dies in an attempt to dynamite the transformer house at the "Sun and Moon" mine.^[19]

• An explosion at a United States Cartridge Company magazine in Tewksbury, Massachusetts, United States, kills 22 employees and local residents; a further 70 people are injured.^[20]

• The 2nd Congress of the Russian Social Democratic Labour Party opens in Brussels, chaired by Lenin.^[21]

• Papal conclave, 1903: The Papal conclave brought about by the death of Pope Leo XIII begins at the Sistine Chapel, Apostolic Palace, in Rome, Italy.