Josh was born and raised in Westport, Connecticut. A Fulbright scholar, he graduated cum laude from Harvard University (where he worked at the Harvard Crimson), and Yale Law School, graduating c. 1984. Josh mentions that one of his classmates was the law professor Akhil Amar. He received a 760 on the verbal section of the SAT, which he has been known to boast about. However, when trying to explain his lack of skill in serious relationships, he claims that his IQ does not "break the bank," so he had to work hard in college, quipping that "by the time [his] roommates notched their 100th party of the year, I think I got my first full night of sleep."
Josh is a non-practicing Jew; his grandfather was held in the Nazi concentration camp Birkenau during World War II. He had an elder sister, Joanie, who died when he was a child. She was babysitting him when a fire broke out in her home and died trying to put out the fire while Josh ran outside - an event which continues to haunt Josh. His father, Noah Lyman, was a and old friend of Leo McGarry. Although Josh thinks his father would have preferred grandchildren to a son in politics, Noah was proud that Josh was working for Bartlet and often bragged about his son to his friends and neighbors. His father died in 1998 on the night of the Illinois primary, after developing an unexpected pulmonary embolism while undergoing chemotherapy for an unspecified form of cancer. His mother splits her time between Westport and West Palm Beach, Florida, before she moves to Florida full-time.