He entered provincial politics in the 1886 Manitoba election, running as a Liberal Party candidate against the Conservative cabinet minister David H. Wilson in the constituency of Dufferin North.

Although Greenway's Liberals won the election with a landslide majority, the new premier was unable to fulfill a campaign promise for the development of local railways.

Many Canadian francophones regarded Greenway's policy as discriminatory, but it was extremely popular with Manitoba's anglophone and Protestant majority.

Greenway's government was re-elected in the 1892 election, and Roblin was personally defeated in the rural constituency, including the town of Morden.

Greenway won another landslide victory in the 1896 election, but Roblin was this time returned to the legislature for the constituency of Woodlands.

Macdonald resigned as premier on October 29, 1900, to run for the Conservative Party of Canada against Clifford Sifton in the federal riding of Brandon.

That consolidation of power reflected Roblin's personal authority over both the government and the provincial Conservative Party: his control over both would be unquestioned for 14 years.

The extent of that victory may be credited to Greenway's leadership of the Liberal Party since he was increasingly uninterested in provincial politics and was spending much of his time looking for a federal patronage appointment.

Like his counterpart James Whitney, in Ontario, Roblin expanded the role of government in Manitoba and promoted many initiatives that would be regarded today as progressive.

McClung made Roblin appear foolish in her famous "parliament of women" parodying the premier's patronizing comments on traditional gender roles.

Roblin also resisted demands to enact a labour code to protect workers and was sometimes reluctant to enforce the province's existing legislation.

When Roblin rejected calls for a formal investigation into the legislative buildings scandal, the Liberal opposition petitioned the Lieutenant Governor to take direct action.

The commission's report concluded that Roblin, Attorney General James H. Howden, and the developer Thomas Kelly had conspired to commit fraud in the contract arrangements.