On February 18, 1840, at age 23, he mentioned in a letter to his fiancée Temperance Blackwell some details of his work in a "neck stock" shirt factory that had been started in Plymouth by his uncle Benjamin.
The two were married in May, 1840, in her hometown of Waterville, Maine, and he apparently returned to work in the Plymouth shirt factory until he sold his share in 1843.
Then in 1847, for $571.47 he bought good-will, press, type, and stock of a local printing business, and in April of that year published the first issue of the Waterville Union, a weekly paper of four pages filled with sermons, religious homilies, and moral stories.
The next day's diary entry reads: "Agreed to go into company in Waterville with [his brother] G.A.H.
It was successful as a shirt maker for well over one hundred years, continuing in operation until 2002, although by the time Hathaway died in 1893, others were in control of the factory and he had no management role.