Joseph was the son of Patrick J. Kennedy, and like his father resided in Boston, Massachusetts. Like his father he became a leading local Democrat and after graduating from Harvard University in 1912 he married Rose Fitzgerald, the daughter of John F. Fitzgerald, the Democrat mayor of Boston.
Like his father, Joseph was a businessman, but was even more successful, becoming a millionaire. Joseph started to build his fortune during World War I. He worked at a shipyard in Quincy, Massachusetts where he oversaw the production of submarines and battleships. He also supervised the construction of housing for shipyard workers and even the onsite cafeteria. In the early 1920's, Joseph acquired two movie studios and personally produced several films, he then sold the companies to the Radio Corporation of America. Joseph multiplied his fortune through stock speculation; he was a master of the stock pool, a then legal stunt in which a few traders conspired to inflate a stock's price, selling just before the bubble burst. Ironically, a short time later he was appointed the first chairman of the Securities and Exchange Commission, where he oversaw the banning of these practices. During Prohibition, Joseph was the US distributor for several British alcohol distillers. He held a US government license to import alcohol for medicinal purposes. He had a large inventory that he sold for a gain of millions of dollars when Prohibition was repealed in 1933. He invested these gains in residential and commercial real estate, the Merchandise Emporium in Chicago and Hialeah Race Track.
Joseph's first exposure to national politics came through Franklin Roosevelt. He donated, loaned, and raised a substantial amount of money for FDR's presidential campaign. President Franklin D. Roosevelt rewarded him, with an appointment as the Chairman of Securities and Exchange Commission. After serving in this post for several years, he resigned in 1935. President Roosevelt then asked him to Chair the Maritime Commission. In 1938, he was appointed as the United States Ambassador to the United Kingdom. Kennedy was a great believer in appeasement and resigned from office in 1940 as he disagreed with Roosevelt's determination to involve the USA in the Second World War.
Joseph had high hopes for political office for his sons, and was grooming his eldest Joseph P. Kennedy, Jr for the presidency. However, Joseph, Jr. was killed whilst on active service in the United States Navy during the war. Joseph then turned his attention to grooming his next eldest son, John F. Kennedy for the presidency, which he won in the 1960 elections.
JFK's assassination in 1963 obviously had a great effect on the family and Joseph was reluctant to support his other son Robert F. Kennedy's bid to become the Democratic nominee for the presidency in the 1968 elections for fear that he might lose yet another child. This fear came to pass when Sirhan Sirhan assassinated Robert F. Kennedy in 1968 while on the campaign trail.
Joseph P. Kennedy, Sr. died the following year, on November 18, 1969.