British General Guy Carleton sent a force composed mostly of Quebec militia in response to news of Allen's crossing of the St. Lawrence.

The American invasion of Quebec began with the arrival at Île aux Noix of the Continental Army under the command of General Philip Schuyler on September 4, 1775.

[9] Before turning command over to Montgomery, Schuyler drafted a proclamation addressed to the people of Quebec, encouraging them to oppose the British and assist the American cause.

On September 8 Ethan Allen and Major John Brown went into the countryside between Saint-Jean and Montreal with a small detachment of Americans to circulate this proclamation, meeting with James Livingston, a Patriot sympathizer at Chambly as well as with the local Caughnawaga Mohawk.

[13] This effort was frustrated by the timely arrival of British troops at Saint-Jean;[14] the exploit made Allen a well-known figure in Montreal and the Richelieu valley.

[17] The remaining forces were distributed among the frontier forts along the Great Lakes, with relatively small garrisons at Montreal, Trois-Rivières, and Quebec City.

By July, Carleton was apparently satisfied with the level of militia support near Montreal,[19] but he did little to stop the activities of the agitators, who also sent reports detailing British military preparations to the Americans.

[21] He also ordered a larger force under Brown's command to secure the area north of the fort, and to cover the road between Saint-Jean and Montreal.

[25] Realizing he would not be able ferry everyone back across the river before troops arrived from the city, Allen chose a wooded area near the Ruisseau-des-Sœurs (labelled on the map above as Ruisseau de la Gde Prairie),[26] between Longue-Pointe and Montreal, to make a stand.

Carleton refused to organize an expedition in relief of Fort Saint-Jean, and the militia members from rural parishes eventually disbanded to attend to their harvests and the defense of their own homes.

He spent about a year, mostly on prison ships, before he was released on parole in British-occupied New York City in November 1776, as the British authorities feared hanging him would create a martyr.

[37][38] Thomas Walker, the merchant to whom Allen had applied for assistance, was arrested in early October 1775 when twenty regulars and a dozen militia came from Montreal to his house in L'Assomption.