Joseph P. Kennedy, Jr. (July 28, 1915–August 12, 1944) was the oldest of the nine children born to Joseph P. Kennedy, Sr. and his wife, Rose Fitzgerald Kennedy. Older brother of future President John F. Kennedy, he was expected to bear the family's political hopes.

Joseph, Jr. entered Harvard University in 1934 and graduated in 1938. There he played football, rugby and was on the Harvard Row team, with captain John Arthur Garber Sr., and served on the student council. He attended Harvard Law School, but left before his final year to volunteer as a Navy flier. He earned his wings in May 1942 and was sent to England in September 1943. He flew missions throughout the winter of 1943-44.

In July 1944, he volunteered for a special mission piloting a modified version of the PB4Y Liberator cargo plane intended to counter the German V-2 rocket attacks on England. The plane was to be loaded with 21,170 pounds (9600 kg) of high explosives, flown across the English Channel, where the pilot and co-pilot would parachute out, and then crash into a German V-2 base. The final crash was to be guided remotely by an escort fighter through radio-control. The pilot and co-pilot were to be recovered by ships in the Channel. Before the pilots ejected, the plane was engulfed in a massive explosion. Kennedy's body was never recovered, and he was posthumously awarded the Navy Cross.

In 1946, the Navy named a destroyer for him, the USS Joseph P. Kennedy, Jr. (DD-850). Among the highlights of its service include the blockade of Cuba during the Cuban Missile Crisis and the afloat recovery teams for Gemini 6 and Gemini 7. It is now a floating museum in Battleship Cove, Fall River, Massachusetts.

Kennedy never married but romantically was linked to at least two women: Edith Bouvier Beale, the beautiful cousin of Jacqueline Kennedy Onassis, and Katharine Mortimer , a New York socialite who declined to become more seriously involved with Joe Jr. because, she claimed, his family was too loud to consider marrying into.