Patrick Gass observed great changes in the United States during his long life. Some of the changes he helped to bring about himself. He was a member of the Lewis and Clark Corp of Discovery. He served as a carpenter, and afterward he was the first of the group to publish a journal of the expedition. He also outlived all the other members of the Corps.

He was born in Falling Springs, Pennsylvania. His parents, Benjamin and Mary McLene Gass, were of Scots-Irish background. His father and grandfather were prominent members of their community and members of the Presbyterian Church. When Patrick was twenty-one years old, he joined the Virginia militia, which was then engaged in fighting Indian tribes. He also worked in the construction business, helping to build the house of James Buchanan, Sr. It was through that job that Gass met and got to know Buchanan's young son, James, Jr., who grew up to become a United States president.

Later, Gass joined the United States Army, serving near St. Louis. Due to this experience living in frontier communities and his military service, Gass was invited to join Lewis and Clark's Corps of Discovery. He entered as a private in early 1804, but was promoted to sergeant when the Corps lost member Charles Floyd to appendicitis in 1804. Gass' carpentry skills were highly valued by the Corps, as he designed and built their three winter headquarters, hewed dugout canoes, and constructed wagons. He also performed any necessary repairs and maintenance of the same.

Once the Corps had reached the Pacific and began their return East, Gass was sometimes given command of the party when Lewis and Clark made investigative explorations away from the larger group. Once the Corps returned home, Gass decided to remain in the army. He served in the War of 1812, during which he lost an eye. He did not marry until age sixty, and when he did it was to a woman four decades younger. Maria Hamilton was twenty-two when she married Gass, and the couple had seven children together.

Despite the great age difference, Gass outlived his young wife. They had settled in Wellsburg, West Virginia, where she died at age thirty-seven. Gass lived on to age ninety-nine. He was the last-surviving member of the Corps of Discovery. His journal was reprinted several times during his life, including English publications as well as French and German translations. The University of Nebraska provides 222 entries from Gass's journal at their Web site.