Bosworth is not as well known in the United States as other Beaux-Arts architects of that time, because his career, under the auspices of John D. Rockefeller, Jr., led him to France in the 1920s, where he was put in charge of the restoration of the Palace of Versailles and Notre-Dame de Reims, projects Rockefeller was interested in and that he generously financed. In time, Bosworth was awarded the French Legion of Honor and the French Cross of the Commander of the Order of Arts and Letters, one of the few Americans ever to receive such honors.
Bosworth was born in 1868 in Marietta, Ohio, and received his architectural training at MIT, one of the leading Beaux-Arts oriented schools in the United States at the time. In 1896, Bosworth left for Paris to study at the famous École des Beaux-Arts. Attending the École was a must for anyone who wanted to make a name for himself in the United States, especially during the years following the World's Columbian Exposition of 1893 in Chicago. Richard Morris Hunt, H. H. Richardson before him as well as Ernst Flagg, Charles McKim, John Merven Carrère, and John Russell Pope, had all studied in Paris. Upon his return to the United States in 1900, Bosworth worked for the firm Carrère and Hastings, which in 1905 was to make a national name for itself with the design of the New York Public Library.
In 1906 Bosworth was called in to design a garden for the prominent philanthropist, the New Yorker Valentine Everit Macy, who lived at Scarborough-on-Hudson. This led to Bosworth’s acquaintance with Frank Vanderlip (1864–1937), president of the City Bank of New York, and former assistant Secretary of the Treasury under President William McKinley. Bosworth designed for Vanderlip a gate for his family estate north of Tarrytown, New York. He also designed a schoolhouse not far from Vanderlip’s estate which is still extant. It is on the Albany Post Road (now Route 9). At about the same time, Vanderlip was appointed to the board of Letchworth Village, an institution for epileptics and the mentally ill founded in 1907. Vanderlip called in Bosworth to lay out the village with its various schools and residences. It is located across the Hudson from Scarborough on a hill not far from the current town of West Haverstraw. For the Rockefellers, he designed Kykuit, transforming a barren treeless site into a lush and spectacular garden.
Around 1911, Theodore Newton Vail (1845–1920) gave Bosworth his largest and most visible commission yet: the corporate headquarters of AT&T, located on a prestigious site in downtown New York City, just a few blocks from Wall Street. It was a modern steel structure clad top to bottom in a Greek-styled exterior, the three-story-high Ionic columns of Vermont granite forming eight registers over a Doric base. In 1913, Bosworth received the commission to design the new campus for MIT in Cambridge, MIT having outgrown its old buildings near Copley Square in Boston. The plan featured a large paved court (now called Killian Court) that is now, however, planted with grass and trees, at the head of which was a domed structure modeled on the Pantheon in Rome. It was at the time the largest non-governmental building in the US.
Although some of Bosworth's subsequent American commissions were office buildings, like the Ocean Cable Office Building (1916) (since demolished), most were houses, estates, and townhouses, like the house for William Barclay Parsons (at 121 East 65th Street) , Philip Gossler (on 14 East 65th Street) in New York, a mansion for Walter Farwell (1920), and house alterations and a garden for Charles A. Stone, both in the Locust Valley area. Vail, who was a great admirer of Italian art and had traveled extensively through Italy, asked Bosworth in 1916 to design his home in Morristown, New Jersey. Bosworth also designed extensive gardens for the house of Samuel Untermeyer, a famous lawyer, in Yonkers, New York. In 1925, he designed the unbuilt Egyptian Museum for Cairo. In 1921, Bosworth built his own house on Long Island next to that of Stone.
Bosworth’s U.S. career, promising as it was, came to an end when John D. Rockefeller Jr., traveling in France in 1922, and appalled at the dire condition of French monuments, set up a fund in 1924 to pay for the restoration of the Palace of Versailles and the Château de Fontainebleau. Bosworth was put in charge of the project. He also took over the restoration of the Notre-Dame de Reims, and in 1935, he founded the University Club of Paris. In 1934, he supervised the restoration of Queen Marie Antoinette’s Trianon cottage near Versailles.
Although Rockefeller's project ended in 1936, Bosworth remained in his adopted country in semi-retirement, building a house for himself and his family, Villa Marietta, in Vaucresson (1935–1936). During WWII, Bosworth was chairman of the Paris committee of the American Volunteer Ambulance Corps. In 1945, he was named associate member of the École des Beaux-Arts. In 1949, he headed a fund drive for restoration of Vimoutiers in Normandy, which had been destroyed by error in a World War II bombing raid. These efforts earned him considerable recognition in France.