He moved back to Grey County, and settled in Markdale, Ontario, where in addition to his medical practice, he also opened a drug store, bought a large cattle farm, and invested in local businesses such as a flour mill and lumber yard.

He also fell in love with Flesher's daughter, Mary Alice, and wooed her by having a beautiful Italianate house that he called Knarsboro Hall built for her in Markdale.

As a Conservative MP, he was a supporter of Canadian Prime Minister Sir John A. Macdonald, but his loyalty to Orangeism led him to differ with his party's leadership on issues of language and religion, particularly on the Manitoba Schools Question.

Following the defeat of the Laurier government in the 1911 election, the new Conservative Prime Minister, Robert Laird Borden, nominated Sproule to the position of Speaker of the House of Commons.

During a thirty-six-day filibuster on the question of the government's naval bill, Sproule lost his patience after weeks of 24-hour sessions, and became the first Speaker ever to "name" a member of the House for disorderly conduct.

Sproule was forced to retire from the Speakership due to ill health, and was named to the Senate of Canada in 1915.