He then attended University College at the University of Toronto, where he earned a B.A. in Mathematics in 1896, with first class standing. While there, he met and became a rival of William Lyon Mackenzie King; the two men, both future prime ministers, did not get along especially well from the start. Meighen then graduated from Osgoode Hall Law School.

In 1904 he married Isabel J. Cox, with whom he had two sons and one daughter. In 1990, one of his grandsons, Michael Meighen, was appointed to the Canadian Senate on the recommendation of Prime Minister Brian Mulroney.

He moved to Manitoba shortly after finishing law school. Early in his professional career, Meighen experimented with several professions, including those of teacher, lawyer, and businessman, before becoming involved in politics as a member of the Conservative Party. In public, Meighen was a first class debater, said to have honed his oratory by delivering lectures to empty desks after class. He was renowned for his sharp wit.

Meighen was first elected to the Canadian House of Commons in 1908, at the age of 34, defeating incumbent John Crawford when he captured the Manitoba riding of Portage la Prairie. In 1911, Meighen won re-election, this time as a member of the new governing party. He won election again in 1913, after being appointed to Prime Minister Robert Borden's Cabinet as Solicitor General (at the time, newly appointed Ministers had to seek re-election).

Meighen served as Solicitor General from June 26, 1913, until August 25, 1917, when he was appointed Minister of Mines and Secretary of State for Canada. In 1917, he was mainly responsible for implementing mandatory military service as a result of the Conscription Crisis of 1917. Noteworthy was the government's decision to give votes to conscription supporters (soldiers and their families), while denying that right to potential opponents of conscription such as immigrants. Meighen's portfolios were again shifted on October 12, 1917, this time to the positions of Minister of the Interior and Superintendent of Indian Affairs.

He was re-elected in the December 1917 federal election, in which Borden's Unionist (wartime coalition) government defeated the opposition Laurier Liberals over the conscription issue.

As Minister of the Interior, Meighen steered through Parliament the largest piece of legislation ever enacted in the British Empire -- creating the Canadian National Railway Company, which continues today. Meighen was re-appointed Minister of Mines on the last day of 1920. In 1919, as acting Minister of Justice and senior Manitoban in the government of Sir Robert Borden, Meighen helped put down the Winnipeg General Strike by force. Though Meighen has often been credited by historians with instigating the prosecution of the Winnipeg strike leaders, in fact he rejected demands from the Citizens' Committee that Ottawa step in when the provincial government of Manitoba refused to prosecute. It took the return to Ottawa in late July 1919 of Charles Doherty, Minister of Justice, for the Citizens' Committee to get federal money to carry forward their campaign against labour.

He became leader of the Conservative and the Unionist Party, and Prime Minister on July 7, 1920, when Borden resigned; Meighen took over the remainder of Borden's mandate. During this first term, he was Prime Minister for about a year and a half.

Meighen fought the 1921 election under the banner of the National Liberal and Conservative Party in an attempt to keep the allegiance of Liberals who had supported the wartime Unionist government. However, his actions in implementing conscription hurt his party's already weak support in Quebec, while the Winnipeg General Strike and farm tariffs made him unpopular among labour and farmers alike. The party was defeated by the Liberals, led by William Lyon Mackenzie King. Meighen was personally defeated in Portage la Prairie, with his party nationally falling to third place behind the newly formed Progressive Party.

Meighen continued to lead the Conservative Party (which had reverted to its traditional name), and was returned to Parliament in 1922, after winning a by-election in the eastern Ontario riding of Grenville.

Despite his party finishing in third place, Meighen became Leader of the Opposition after the Progressives declined the opportunity to become the Official Opposition. Meighen's term as opposition leader was most marked by his response to the crisis at Chanak, in which British Colonial Secretary Winston Churchill leaked to the newspapers that the Dominions might be called upon to help British forces in the Chanak area, far away in Turkey. With Parliament not in session, King refused to commit to sending troops, resenting the way Churchill had gone over the Dominion leaders' heads. King used the rationale that Parliament should decide, and that the matter was not important enough to recall Parliament. Meighen strongly condemned King's action, stating in a Toronto hotel and quoting former Liberal PM Wilfrid Laurier, "When Britain's message came, then Canada should have said, 'Ready, aye ready, we stand by you.'" The crisis subsided within days, and Meighen was left with a reputation as being blindly in favour of Britain's interests. The matter brought down the government of British Prime Minister David Lloyd George.

Unlike Laurier and Borden, who got along well on a personal level despite being leaders of opposing political parties, there existed between Meighen and King a very deep personal distrust and animosity. Meighen looked down upon King, whom he called "Rex" (King's old University nickname), and considered him unprincipled. Their personal rivalry, bitter and unrelenting, was probably the nastiest in the history of Canadian politics.

The Liberal government of Mackenzie King was soon beset with scandals and corruption. Much of this was uncovered in a Royal Commission established to probe wrongdoing in Quebec, and in particular, in connection with the construction and expansion of the Beauharnois Canal, leading to the Beauharnois Scandal. The Tories won a plurality of seats in the inconclusive election of 1925, but King was able to retain power until mid 1926 through an alliance with the Progressives. Meighen denounced King for staying in power, saying he was holding onto office like a "lobster with lockjaw." Another corruption scandal, this time in the Customs Department, was soon discovered, making the Progressives even more wary of continuing their support for King.

Because of the possibility of losing a vote in the Commons, due to insufficient numbers, while Meighen and his ministers were in the process of being re-elected (a relic of British law dating to 1701 that was repealed in Canada in 1938), Meighen advised that the Governor General make the ministers of the Crown "acting" only, and not take the oath of office. King created an uproar about this tactic, attracting Progressive support to take down the government. In the event, the government lost the confidence of the House by one vote. With no other parliamentary grouping to call upon, Byng called the Canadian federal election, 1926. Meighen's party was swept from office, and Meighen himself was again defeated in Portage la Prairie. His second term as PM lasted just three months.

Meighen resigned as Conservative Party leader shortly thereafter, and moved to Toronto to practice law.

Meighen was appointed to the Senate in 1932 on the recommendation of Conservative Prime Minister R.B. Bennett. He served as Leader of the Government in the Senate and Minister without Portfolio from February 3, 1932, to October 22, 1935. He served as Leader of the Opposition in the Senate from 1935 until he resigned from the upper house in January 1942.

In late 1941, Meighen was prevailed upon by a unanimous vote in a national conference of the party to become leader of the Conservative Party for the duration of the war. He accepted the party leadership on November 13, 1941, foregoing a leadership convention, and campaigned in favour of conscription, a measure which his predecessor, Robert Manion, had opposed. As leader, Meighen continued to champion the concept of a National Government including all parties, which the party had advocated in the 1940 federal election. Such an arrangement had been seen in Canada during World War I, and was also used in Britain during World War II. However, Canadians did not support this idea.

Meighen, lacking a Commons seat while leading the main Opposition party, resigned his Senate seat on January 16, 1942, and campaigned in a by-election for the Toronto riding of York South, to return to the Commons. His candidacy received the improbable support of the Liberal Premier of Ontario Mitchell Hepburn; this act effectively hastened the end of Hepburn's Liberal Premiership, and did not in any case grant Meighen durable electoral support. According to custom, the Liberals did not run a candidate in the riding. Still harbouring a deep hatred for the Conservative leader and thinking that the return to the Commons of the ardently conscriptionist Meighen would further inflame the difficult, smouldering conscription issue (which two years later led to the conscription crisis), King arranged for campaign resources to be sent to the Co-operative Commonwealth Federation's Joseph Noseworthy.

The absence of a Liberal candidate actually hurt Meighen's chances by precluding the possibility of a split in the anti-Conservative vote, and Meighen was defeated in the February 9, 1942 vote. With its leader excluded from the Commons, the Conservative Party was again weakened. Meighen continued to campaign for immediate conscription as part of a "total war" effort through the spring and summer, but did not again seek a seat in the House of Commons. In September, Meighen called for a national party convention to determine the party's policies and "broaden out" the party. It remained unclear whether Meighen sought to have his leadership confirmed or to have his successor chosen. As the convention neared, news sources reported that Meighen had approached Manitoba's Liberal - Progressive Premier John Bracken about seeking the leadership, and that the convention would adopt a platform that would move the party towards the left. Meighen announced in his keynote address to the party on December 9, 1942 that he was not a candidate for the leadership and the party subsequently chose Bracken as leader, and renamed itself the Progressive Conservative Party of Canada.

Following his second political retirement, Meighen returned to the practice of law in Toronto. He died in Toronto, aged 86, on August 5, 1960, and was buried in St. Marys Cemetery, St. Marys, Ontario, near his birthplace. As of 2011, he has had the longest retirement of any Canadian Prime Minister, at 33 years, 10 months, 11 days.

There are schools in St. Marys, Ontario and Portage La Prairie, Manitoba named for Arthur Meighen. Mount Arthur Meighen is a 3205 m (10515 ft) peak located in the Premier Range of the Cariboo Mountains in the east - central interior of British Columbia, Canada. The mountain is south of the head of the McClennan River and immediately west of the town of Valemount, British Columbia. Meighen Island, in the far north of the Canadian Arctic, is named after Arthur Meighen. The federal government building in Toronto's Yonge and St Clair area is named for him.

Meighen ranks as #14 out of the 20 Prime Ministers through Jean Chrétien, in the survey of Canadian historians included in Prime Ministers: Ranking Canada's Leaders by J.L. Granatstein and Norman Hillmer.