Nicholas enlisted in the Army in November of 1999, attended Army Basic Combat Training, and went on to serve for 22 years on active duty. He has been stationed in numerous locations, such South Korea, Washington State, Oklahoma, Texas, Kansas, Maryland, and North Carolina. He retired in June of 2022 at the rank of First Sergeant (1SG).

While stationed at Washington, Nicholas was deployed to Iraq where his unit was assigned the Counter Rocket, Mortar, and Artillery (C-RAM) mission. He served as a Land-based Phalanx Weapon System (LPWS) Section Sergeant for the duration of his deployment to the CENTCOM Area of Responsibilities (AOR). Upon his redeployment 1SG Martinelli was reassigned to the Noncommissioned Officers Academy, Fort Sill, OK, where he served as the Senior Small Group Instructor for the Advanced Leader Course from 2009-2011.

In 2011, he was assigned to E Battery, 4-5 AMD, where he served as the Battery First Sergeant and a Platoon Sergeant from 2011-2013. In 2014, he was reassigned to C Battery 5-5 ADA, JBLM, WA where he served as an LPWS Platoon Sergeant from 2013- 2014. His unit was deployed to Camp Dahlke, Afghanistan where they performed a C- RAM mission. He returned to JBLM in March of 2015, where he was reassigned as the unit First Sergeant for B Battery, 5-5 ADA.

In October of 2016, six months after just returning from Afghanistan, he and his unit were deployed to two locations in Iraq, where they performed C-RAM missions at each location. His unit was selected as the Knox Award winner, which is given to the top ADA unit in the Army for their performance throughout 2015.