After graduating St. Columbkille School, Kelly joined the U.S. Air Force and left for basic training at Lackland AFB, on July 1, 1961, aged 17. After, he was deployed to what was then Formosa, where he started his radio career in Armed Forces Radio. After returning to the United States he was stationed in Maryland. Upon his honorable discharge from the US Air Force, he took a job with Metropolitan Life Insurance and married Michele Larichiuta in 1964.
In 1967, the family moved to Brighton, Massachusetts, where he worked for Ross Laboratories. In 1968, he joined WCAS (AM) as a reporter and producer of documentaries. In 1969, while working for WEZE, Kelly won an area wide reputation for hard hitting investigative reporting, including the first story on Senator Edward Kennedy's involvement in the Chappaquiddick incident three hours before any other station in the country had the story. In 1970, he joined WBZ (AM) News, where he significantly contributed as investigative reporter for several years, earning awards for excellence in reporting from United Press International. Kelly joined WNAC-TV in 1974 as an investigative reporter.