Nathan Gammon was born on May 19, 1803, at Mount Pleasant, Sullivan County, Tennessee in the far northeastern corner of the state. He grew up in the midst of a prestigious social circle that included close friends and future Presidents Andrew Jackson, Andrew Johnson, and James Knox Polk, and both his father and grandfather were active in Tennessee politics.
As a young man, Nathan Gammon studied law and did practice it, but he also apparently had no political ambitions, and declined to run for public office on more than one occasion, despite the urging of close friends such as Polk. He went into business instead, becoming a very successful merchant, first in Jonesboro, and later in Knoxville.
On July 20, 1824, he married Mary Erwin Hamilton, also a native of Sullivan County, Tennessee. They initially made their home in Jonesboro, where their six children were born: Elizabeth Hamilton Looney, William Hamilton, Jane Leticia (“Jennie”), Joseph Hamilton, George Alexander, and Mary Imogene. With the exception of Mary, all the children survived into adulthood.
In November of 1851, Nathan Gammon moved his family from Jonesboro to Knoxville, which was rapidly becoming a terminus for seamboat navigation and a center of trade for eastern Tennessee. Steamboats were the primary method of transport until the railroad arrived in 1854, and Gammon proved adept at the occupation of commission merchant. He developed a large freighting business that operated out of a warehouse on the Tennessee River at the foot of Gay Street. His eldest son, William, eventually went into business with him as an assistant.
Gammon anticipated the changes railroad transportation would bring, and became the first Passenger and Freight Agent for the East Tennessee, Virginia & Georgia Railroad when it arrived in the city. Skills acquired in that position, and experience as a stenographer, later earned him an appointment as Clerk of the District Court of the United States.