[2] His younger brother was Leonard Gansevoort, who was more active politically, serving in the state assembly and senate, as well as the Continental Congress.

[8][3] As the American Revolution grew closer, Peter Gansevoort joined the Albany County militia.

Lieutenant Colonel Peter W. Yates had been the regiment's primary field commander, but remained as commander of Fort George when Major Gansevoort led much of the regiment north with Richard Montgomery's forces for the invasion of Quebec (1775).

In late October, to improve the effect of the siege, Montgomery sent Gansevoort and his men down the river to seize Fort Chambly.

He started on the advance to Quebec City, but by the time the force reached Trois-Rivières, he was being carried on a stretcher.

[9] Gansevoort had recovered to the point where he led the remaining New York forces south in a fighting withdrawal that stopped the British advance at Lake Champlain.

They hurriedly set up a garrison, getting the last boatload of supplies into the fort under fire from St. Leger's advance force on August 2.

[2] He and his more than 700-strong garrison withstood the three-week-long siege, making a sortie on August 6, while much of St. Leger's force was occupied in the Battle of Oriskany.

[10] The siege was lifted on August 22, after word arrived that Benedict Arnold was leading a large relief force up the Mohawk Valley.

[6] He received the grateful thanks of the Congress, as John Adams noted that "Gansevoort has proven that it is possible to hold a fort.

In 1790,[2] he served for a while as sheriff of Albany County, as a commissioner of Indian affairs, and continued his support of the military in the militia and as a quartermaster.

Over the years, they had five children, five of whom lived past infancy, including:[10] He died at home in Albany on July 2, 1812.

[12] His grandson through his son Leonard was Guert Gansevoort, who had a distinguished naval career that spanned 45 years.