A 1795 account of his life asserts that he had “more information of the nature and properties of the indigenous plants and vegetables, than any other man in the country” and “administered relief in many cases, where no other medical assistance could at that time be procured.”[8] In 1763, Warner's father purchased land in Bennington, now in the state of Vermont, a town that was chartered by a grant from the colonial governor of New Hampshire, Benning Wentworth.

Commanding the Bennington militia, Warner fortified Breakenridge's house and property against a large posse from Albany, New York, sent to evict the settler.

[14] On May 8, 1775, a council of officers appointed Warner third in command after Ethan Allen and James Easton of Pittsfield, Massachusetts, of an expedition to capture Fort Ticonderoga.

But Warner and the men he had recruited were left on the east shore of Lake Champlain as a rear guard while Allen and newly arrived Colonel Benedict Arnold surprised the garrison on the morning of May 10.

During the following winter, artillery colonel Henry Knox, acting under orders from George Washington, hauled guns from Lake Champlain to Boston.

(See Noble train of artillery)[16] Following the capture of the forts, Warner accompanied Allen to St. John (today's Saint-Jean-sur-Richelieu, Québec), a British outpost on the Richelieu River, the outlet of Lake Champlain.

"[18] Although New York was hesitant to incorporate men who had opposed them in the land dispute, the provincial congress established the regiment under the command of a lieutenant colonel and a major.

[23] In the late summer and fall of 1775, an American army under command of Philip Schuyler and then Brigadier General Richard Montgomery invaded Canada by way of Lake Champlain.

In mid-September, Warner and his regiment saw action near Fort St. John before being stationed along the St. Lawrence River where they kept watch on Montreal and the British shipping.

On October 30, Governor General Guy Carleton and approximately 800 men in 35 to 40 boats attempted to cross the St. Lawrence and relieve Fort St. John.

They crossed the length of frozen Lake Champlain to St. John, visited Montreal for supplies, and then headed east to Quebec, a distance of at least 400 miles (640 km).

Details of Warner’s role are scanty, but in a 1795 sketch of his life, pastor and newspaper editor Samuel Williams wrote, “Warner chose the most difficult part of the business, remaining always with the rear, picking up the lame and diseased, assisting and encouraging those who were the most unable to take care of themselves, and generally kept but a few miles in advance of the British, who were rapidly pursuing the retreating Americans from post to post.

By steadily pursuing this conduct he brought off most of the invalids; and with his corps of the infirm and diseased he arrived at Ticonderoga, a few days after the body of the army had taken possession of the post.”[35] On July 5, 1776, the Continental Congress resolved that “a regiment be raised out of the officers who served in Canada” with Seth Warner as colonel.

[36] On July 24, Warner attended a convention in Dorset, one of a series of meetings held as the New Hampshire Grants gradually formed an independent government.

Warner and all but one delegate pledged "at the Risque of our Lives and fortunes to Defend, by arms, the United American States against the Hostile attempts of the British Fleets and Armies, until the present unhappy Controversy between the two Countries shall be settled.

In September, Warner and captains Wait Hopkins and Gideon Brownson traveled to Philadelphia to petition the Continental Congress to reimburse them for expenses from the Canada campaign.

[41] As an army of 8000 under command of Lieutenant General John Burgoyne sailed south on Lake Champlain, Warner's men joined the fatigue parties to prepare the forts for attack.

In late June, commander Major General Arthur St. Clair ordered Warner to raise the militia of the New Hampshire Grants to counter Indian raids along Otter Creek.

[42] On July 1 from Rutland, Vermont, Warner wrote to the leaders of the independent state, then meeting in a constitutional convention in Windsor on the Connecticut River, calling upon them for men and supplies.

"[47] About 1100 men were under his command: his own regiment, Francis’s handpicked rearguard, the Second New Hampshire under Colonel Nathan Hale, and several hundred sick and stragglers, who camped in a valley by a small stream.

The main battle took place on Monument Hill where the advantage seesawed back and forth until the arrival of German troops from the Duchy of Brunswick under command of Major General Friedrich Adolf Riedesel.

[50] Following the Battle of Hubbardton, Warner and his regiment guarded the frontier north of Manchester, Vermont, with orders from Schuyler to seize cattle and carriages and to arrest "Tories" (Loyalists).

The American victory seemed to be complete and the exhausted militia had turned to celebration when more than 600 German reinforcements under Lieutenant Colonel Heinrich Breymann advanced from the west.

a single time.”[58] Warner's regiment and Vermont ranger companies participated in a raid upon Ticonderoga and Mount Independence, using the outpost in Pawlet as a staging area.

In the late 1770s and early 1780s, Ethan Allen, who had spent three years as a prisoner of war, his brother Ira, and Governor Thomas Chittenden dominated Vermont politics, and Warner's influence waned.

Loyalist and British negotiator Justus Sherwood warned his superiors, “I fear the Benningtonites, especially the two mob Colonels; Warner and [Samuel] Herrick, will find means to overturn the whole system.

[75][76] Prominent nineteenth-century Vermont writers, including Rowland E. Robinson, argued that in honoring its early heroes the state had neglected Warner.

[77] Under the fictional name of Charles Warrington, Warner was the hero of the popular romance The Green Mountain Boys, published in 1839 by Daniel Pierce Thompson.

In the preface to the second edition of this novel, Thompson wrote that if he could he would make several changes "particularly in the appellation of one of the most conspicuous personages, Charles Warrington, whose prototype was intended to be the chivalrous Colonel Seth Warner.

[84] The United States Army's Large Tug MOD (LT-128 Class) 5500 HP tugboat number LT-806 is named the COL Seth Warner.