Kinnear was born in Logansport, Indiana, to Suzanne (née Buck), a homemaker, and Edward Kinnear, a career diplomat who worked for the US State Department. He has two brothers, James (born 1957) and Steven (born 1959). He is of Scots-Irish descent. Kinnear grew up a "Foreign Service brat", having moved around frequently, from Beirut to Athens. While a student at the American Community Schools in Athens, Kinnear first ventured into the role of talk show host with his radio show School Daze With Greg Kinnear. Returning to the United States for a university education, he attended the University of Arizona, graduating in 1985 with a degree in broadcast journalism. While there, he was a member of the Alpha Tau Omega fraternity.