During the Alberta and Great Waterways Railway scandal, he was a leader of the Liberal insurgency that forced Premier Alexander Cameron Rutherford from office.

[7] In 1905, Boyle ran in Alberta's inaugural provincial election as the Liberal candidate in Sturgeon, where he defeated Conservative Frank Knight by a wide margin.

"[11] He also sided with the government in its rejection of Conservative demands that it build and operate railways, as he felt that doing so would not be viable as long as the trunk lines were in private hands.

[12] He enthusiastically backed private construction of railways, however, and greeted the announcement of the Alberta and Great Waterways Railway—which was to run northward from Edmonton to Lac la Biche and later Fort McMurray—with what historian L. G. Thomas describes as "an extravagant eulogy...[speaking] of Lac la Biche as another Lake Louise, of Pullmans running from New Orleans to the Arctic circle, and of northern Alberta as a second Cobalt region.

Woods, deputy to Attorney-General Charles Wilson Cross, had removed key components from the government's files on the A&GWR, in advance of their having been inspected by Boyle and Conservative leader R. B.

[17] In the ensuing debate, several charges were levelled against Boyle himself: Agriculture Minister Duncan Marshall accused him of being motivated by his rejection for the position of A&GWR solicitor.

[18] The Edmonton Bulletin accused him of approaching two Liberal members who were also hotel keepers, Lucien Boudreau and Robert L. Shaw, and offering them immunity from prosecution for liquor offenses if they helped bring down Rutherford's government and replace it with one, led by Cushing, in which Boyle would be Attorney-General.

[19] Though Rutherford survived a motion of non-confidence (moved by Ezra Riley and seconded by Boyle) by three votes,[19] he was successfully pressured to resign by Lieutenant-Governor of Alberta George Bulyea.

It had been expected that Cushing would replace Rutherford if the latter was defeated, but Bulyea and other prominent Liberals did not have confidence in him, and instead selected Arthur Sifton, Alberta's Chief Justice.

[20] Sifton left all major figures of the A&GWR affair, including Boyle, out of his first cabinet, and instead appointed fellow judge Charles R. Mitchell Attorney-General.

[22] The law required that members newly admitted to cabinet resign their seats in the legislature and immediately contest a by-election; Boyle was re-elected in Sturgeon by a safe margin.

[23] Boyle's time as Education Minister was tumultuous: many teachers enlisted to fight in World War I, and many others left the profession for more lucrative opportunities elsewhere.

[28] In 1918, new premier Charles Stewart, who had succeeded Sifton when the latter entered federal politics in 1917, fired Cross and appointed Boyle Attorney-General.

In the assessment of Lakeland College historian Franklin Foster, Boyle "showed vigour" in the legislature, where he presented a strong opposition to the new UFA government of Herbert Greenfield.

[35] Even so, he showed some private courtesy: when John Edward Brownlee, Greenfield's Attorney-General and his strongman in the legislature, missed a session due to illness, Boyle assured him that the Liberals would not attack the government too vigorously in his absence.

[36] As leader of the Alberta Liberals, Boyle corresponded extensively with Liberal Party of Canada leader (and Prime Minister of Canada) William Lyon Mackenzie King; according to Foster, Boyle's letters to King were "a mixture of useless information and pleas to be rescued by an appointment to the bench.