Beginning in the hardware trade, he expanded into steamship transportation on the River St. Lawrence and then banking.
He initially supported the reform measures of Louis-Hippolyte LaFontaine, but gradually became more radical, ending his political career as member of the Parti rouge and calling for the voluntary annexation of Canada to the United States.
[1][2] De Witt married Sophronia Frary of Montreal on January 12, 1816, in the Anglican church in Dunham township.
The Banque was designed to provide easier access to credit for the petit bourgeoisie, farmers and artisans of Lower Canada, breaking the Bank of Montreal's monopoly.
Of liberal and reform tendencies, he supported the Parti patriote led by Louis-Joseph Papineau and Denis-Benjamin Viger, and their challenges to the appointed Governor of Lower Canada.
In the general elections in the fall of 1834, De Witt was re-elected in Beauharnois with a comfortable margin, part of a major victory by the Parti patriote across the province.
Eventually, De Witt and the other partners felt it necessary to publish a sworn deposition, denying that the Bank du Peuple had "lent or supplied funds for the purpose of purchasing arms, in order to destroy and subvert Her Majesty's Government in this Province".
De Witt's position as a member of the Legislative Assembly ended on March 27, 1838, when the suspension came into force.
In 1843, when all but one of the members of the Executive Council resigned in a dispute with the Governor General, Sir Charles Metcalfe, De Witt joined in the motion passed by the Assembly condemning Metcalfe and supporting LaFontaine, Robert Baldwin, and the other ministers.
[1][12] In the lead-up to the 1844 general elections, De Witt joined campaign functions by the reform groups.
He was re-elected and became part of a group of "English" Liberals in the Assembly, who generally supported LaFontaine on major issues.
De Witt and the "English" Liberals supported the victorious LaFontaine–Baldwin ministry, including in the vote over the Rebellion Losses Bill.
When it received royal assent by Governor General Lord Elgin, Tories rioted in Montreal and burnt the Parliament building.
[1][2][13][14] In the last session before the general elections of 1851, De Witt was one of a small group of members who supported the idea of Canadian independence.
In the general elections of 1851, De Witt was defeated by a more moderate reformer, Ovide Le Blanc.
[1] In 1846, as part of its move to free trade, the British government repealed the Canada Corn Act 1843, which had given an imperial tariff protection to Canadian grain exports to Britain.
In response, a movement for voluntary annexation of Canada by the United States began, particularly amongst the Montreal business community.