Beaver's introduction to commerce began when he took a job at a store owned by his father in New Berlin, Pennsylvania.  A year later, he left his father's store to work for the Reverend Jasper Bennett in Williamsport.  As an employee of Bennett, Beaver often traveled to Philadelphia to make purchases, and he soon made the acquaintance of many prominent merchants in the city.  As a result of such connections, in 1837, Beaver was hired by the firm of Bray and Bancroft in Philadelphia.   Just three years after being hired at Bray and Bancroft, Beaver became a full partner in the firm, a position he held until 1857, at which point he became a trustee of the Danville Iron and Steel Works.  Beaver enjoyed success as a trustee, and in 1859, he and fellow trustee Isaac Waterman purchased the works.  He remained a co-owner until 1876, when he sold his holdings and retired. 

While an employee of Bray and Bancroft, Beaver had met  Elizabeth Wilkins, and they had married on January 23, 1838.  Together they had seven children, two of whom were lost in childhood.  His wife died on December 27, 1884.  Beaver remained an active member of the Danville community until his death.  Generosity marked his later life was marked.  In 1888, thanks to a donation from Beaver, Danville erected the Thomas Beaver Free Library and YMCA Building and celebrated its opening with fireworks and a parade.  Additionally, in 1889, Beaver donated $30,000 dollars to Dickinson College, with the money used to endow the Thomas Beaver Chair of English Literature.  On May 19, 1891, Beaver died, survived by five children.  He is buried with his wife in Lewisburg, Pennsylvania.