 After graduating from Harvard University in 1876, he studied architecture at the Massachusetts Institute of Technology and the École des Beaux-Arts in Paris, then worked as senior draftsman in Henry Hobson Richardson's office.After Richardson's death in 1886, Longfellow teamed up with Frank Ellis Alden (1859-1908) and Alfred Branch Harlow (1857-1927) to found the firm of Longfellow, Alden & Harlow, with offices in Boston and Pittsburgh.The firm designed the Carnegie Library of Pittsburgh and the City Hall in Cambridge, Massachusetts.