Jack was born in 1925 in Boston, and attended the Phillips Andover Academy, graduating in 1943. His father was the president of a doughnut company, and Jack's upbringing was comfortable.
He attended Harvard and graduated with a degree in War Service Sciences, as well as a stint as the President of the Hasty Pudding Club. He joined the Navy, and served as an Ensign. He was a communications officer on the USS Lake Champlain in the Naval Reserve during World War II.
His first movie was in 1954, in It Should Happen to You, and his career went from strength to strength.
Jack Lemmon was married to Cynthia Stone from 1950 until 1956. He then married Felicia Farr and was married to her from 1962 until his death in 2001. He had two children (Courtney and Christopher).