Washburn was educated in the academies at Hancock and Westminster, and then attended Yale College, graduating in 1844. He was a member of the Skull and Bones Society. He was employed as a store clerk from 1844 to 1847 in the business of his uncle in Orange. He established a chair factory in Erving, operating it from 1847 to 1857 and parlaying a $10,000 ($ in dollars) investment into a wood products business whose annual production exceeded $150,000 ($). In 1849 he cofounded the Franklin County Trust Company, on whose board he sat until 1858. He moved to Greenfield in 1857, where he was elected president of the Greenfield Bank (later the First National Bank), a post he would hold for the rest of his life.