Shawn M. O’Neil was born in November 1962. He was a 1981 graduate of Trinity High School. Shawn served in the U.S. Marine Corps as a corrections specialist and was stationed at Camp Lejeune in Jacksonville, North Carolina, and at Pearl Harbor in Honolulu, Hawaii. He received an honorable discharge in 1989, at the rank of Sergeant. During his service to his country, he earned several honors, including the Meritorious Unit Commendation, the Good Conduct Medal, the Meritorious Mast, the Rifle Expert Badge and the Pistol Sharpshooter Badge.

After returning to New Hampshire, Shawn dedicated 20 years as a correctional officer in the N.H. State Prison System and was a member of their SERT team. For his exceptional bravery in saving the life of an inmate, he was awarded the Medal of Honor by the State of New Hampshire. In addition to his law enforcement career, he also refereed floor hockey at Tollbooth Sports in Hooksett, N.H. Shawn was an avid sportsman throughout his life and played team hockey, football and baseball. He enjoyed hunting, fishing, biking, reading, bird watching, hiking and spending leisurely days at the lake.