He briefly worked with Benedict Arnold during the Revolution

One day, each of these men will understand what it was like to be the most infamous person in America. Colonel Benedict Arnold commanded a group of American troops who traveled from Massachusetts to Quebec City via Maine in 1775. Around 1100 men made the trip in total, Burr included. The impressed colonel remarked to the future vice president as they were traveling, calling him "a young gentleman with much vitality and activity, who has performed with remarkable spirit and resolve on our fatiguing march." A tiresome march, for Arnold, had greatly misjudged the difficulty of the journey, and by the time they arrived at their target, 500 or so of his men had fled, perished, or been captured.

A telegram for General Richard Montgomery, who had conquered Montreal and was his route to Quebec City with his force of 300 soldiers, was delivered to Burr at the end of this northward march. Burr immediately won over Montgomery, who then hired him as his aide-de-camp. However, their working relationship would soon come to an end.

The commander was killed by a cannon burst on December 31, amid a blizzardy winter fight, outside the city. Later, several eyewitnesses said that Burr had unsuccessfully attempted to remove his commander's body from the battlefield, although historians have their concerns about this claim.