Knight co-founded the large and famous brand, Fruit of the Loom. Knight worked on the family farm until he was 18 and went to work at Sprague Print Works in Cranston, but eventually returned to farming. In 1835 he opened a general grocery store near the print works.
After buying out Penniman, Knight continued alone for about four years until 1849 when he sold his grocery business to Jeremiah.
In 1852 Knight sold half of his flour and grain interest to Robert Knight, another brother. He then purchased from Robert a one-half interest in the Pontiac Mill and Bleachery, and the firm of B. B. and R. Knight was formed.
The brothers later began to focus solely on the textile manufacturing. The company became the largest textile manufacturer in the world.
Knight also became involved in various banking and insurance companies.
Benjamin Knight also served as in several political offices, including as a member of the General Assembly and city alderman.