In the 1830s, McIntosh was chairman of the Committee of House District Reformers. From 1832–1833 McIntosh was chairman of the Central Committee of One Hundred Freeholders of Upper Canada, a group that organized opposition to the provincial government of Upper Canada. In 1833 McIntosh married his second wife, Helen Ferguson ( Baxter) and they would have at least seven children together. In 1834, McIntosh was elected in the 4th riding of
York as a
Reformer to the Upper Canadian legislature. He was reelected in 1836. He chaired a meeting in 1837 where Toronto reformers called on Upper Canadians to organize groups to oppose the provincial administration. In the fall of 1837, Mackenzie invited McIntosh to a meeting of reformers where Mackenzie proposed the
Upper Canada Rebellion. Mackenzie's proposal was rejected and McIntosh did not participate in the rebellion. In 1841 McIntosh ran for the
1st Parliament of the Province of Canada in the 4th riding of York. Reformers asked McIntosh to not run in the election and
Robert Baldwin declared his intention to run in the same seat. McIntosh refused to quit the race so his reform colleague could be more easily elected and did not attend the election hustings in Newmarket. Baldwin won the election without opposition. Baldwin was also elected in Hastings, so a by-election was called in the riding and McIntosh stood as a candidate again. He attended the hustings but was defeated by
Louis-Hippolyte Lafontaine in a vote of 186-52. In 1849, he allowed
William Lyon Mackenzie to stay at his home upon Mackenzie's return to Toronto. That evening a mob assembled at the McIntosh property and burned an effigy of Mackenzie. McIntosh asked the Toronto City Council for help protecting him and his property. Many city councilors suggested that McIntosh should ask Mackenzie to leave his home, and the council passed a declaration saying the people would only be rioting at McIntosh's home if they were "deeply insulted" over the situation. Reformers encouraged McIntosh to run in the 1851 provincial election in the 4th riding of York, but McIntosh decided to support the Reform candidate
Joseph Hartman. McIntosh was ill in the last years of his life, limiting his political activities. He died in Toronto on July 3, 1853. ==Philosophy and views==