Arthur Lewis Watkins Sifton was born on October 26, 1858, near St. Johns, Middlesex County, Canada West (Ontario). His father, John Wright Sifton, was a Speaker of the Legislative Assembly of Manitoba and president of the Manitoba Free Press Publishing Company. His mother was Kate Watkins, and his younger brother, Sir Clifford, was prominent in Manitoba and federal politics. Sifton was a Wesleyan Methodist.

Sifton was educated at various public schools in Ontario: Wesley College, Winnipeg, Manitoba; and, Victoria University, Cobourg, Ontario (later located in Toronto). In 1880, he received a Bachelor of Arts degree from Victoria University, then a Master of Arts degree by the same school in 1888, and finally a Bachelor of Laws degree by the University of Toronto later that same year.

In 1882, Sifton married Mary H. Deering of Cobourg, Ontario. Together, they had two children: Nellie Louise and Lewis Raymond St. Clair.

In May of 1880, Sifton began studying law in Winnipeg, and was admitted to the Manitoba Bar in 1883. In the early 1880s, he practiced law with his brother Clifford in Brandon, Manitoba. He then practiced in Prince Albert, North-West Territories, from 1885 to 1888, and after 1889, in Calgary, North-West Territories (later known as Alberta).

In 1882, Sifton was elected to the first City Council of Brandon. In 1889, after moving to Calgary, he was elected to the Legislative Assembly of the North-West Territories as the Member for the electoral district of Banff. From 1901 to 1903, he served as the Territorial Commissioner of Public Works.

In 1903, Sifton was appointed Chief Justice of the Supreme Court of the North-West Territories by Prime Minister Sir Wilfrid Laurier. After the Province of Alberta was established in 1905, he was appointed as the first Chief Justice of the Supreme Court of Alberta in 1907. He resigned as Chief Justice and was appointed Premier of Alberta on May 26, 1910, by Lieutenant Governor George H. V. Bulyea. Sifton was elected the Member for Vermilion in a by-election held on June 29, 1910, and his Liberal government was re-elected in the general elections of 1913 and 1917.

Alongside his duties as Premier, Sifton also served the Province of Alberta as Provincial Treasurer (1910-1912, 1913), Minister of Public Works (1910-1912), and Minister of Railways and Telephones (1911-1917). As Premier, Sifton expanded railway service and promoted the transfer of control over natural resources from the federal government to the provincial government. He held office in 1916, when white and black women were given the right to vote in Alberta. Following a plebiscite in 1915, the Sifton Government enacted legislation in 1916 that severely restricted the sale, distribution, and consumption of alcoholic beverages.

On October 30, 1917, Arthur L. W. Sifton resigned as Premier of Alberta in order to join the federal Union Government of Prime Minister Sir Robert L. Borden. In the general election of December 17, 1917, Sifton was elected Member of Parliament for Medicine Hat, Alberta, and was appointed Minister of Customs that same year. In 1919, he was appointed Minister of Public Works and Secretary of State, and served as a member of the Canadian delegation to the Paris Peace Conference. In 1920, he was appointed to the Privy Council of the United Kingdom.

Sifton's honours include: King's Counsel (April 23, 1902) and an Honourary Doctor of Civil Laws degree, University of Alberta (1908). In 1911, he represented Alberta at the coronation of King George V, King of the United Kingdom and the British Dominions, and Emperor of India (1910-1936).

Arthur L. W. Sifton died on January 21, 1921, in Ottawa, Ontario, and was buried in the Beechwood Cemetery. A boulevard in the city of Calgary and an elementary school in Edmonton were named in his memory.