2ndLt Andrew Hornfeck was commissioned in 2006.  After graduation from The Basic School and Infantry Officer Course, he received orders to 3d Battalion, 8th Marines.  As a rifle platoon commander, he deployed with the 22d Marine Expeditionary Unit and supported disaster response in Bangladesh.  As a weapons platoon commander, he deployed with Special Purpose MAGTF—Afghanistan and conducted combat operations in Helmand and Farah Provinces.  As an assistant operations officer, he conducted pre-deployment training with the 26th Marine Expeditionary Unit before receiving follow-on orders.

In 2010, Captain Hornfeck reported to The Basic School for duty as a warfighting instructor. While there, he served as a platoon tactics instructor, a staff platoon commander for two Basic Officer Courses, and the director of instructor education.  Following this tour, he attended Expeditionary Warfare School.

Captain Hornfeck reported for duty to 2d Battalion, 2d Marines in the summer of 2014.  Over the following 28 months, he served as a company commander during deployments to Morón, Spain, for Special Purpose MAGTF—Crisis Response—Africa; Al Qwerah, Jordan, for Exercise EAGER LION; and Okinawa, Japan, as part of the Unit Deployment Program.  His company participated in a military assisted departure in Tripoli, Libya; humanitarian aid operations in Monrovia, Liberia; and theater security cooperation exercises in Malaysia, Thailand, and the Philippines.  Following his next promotion, Major Hornfeck executed orders to 8th Marine Regiment for duties as the Headquarters Company Commander.

In June 2017, Major Hornfeck assumed command of Marine Corps Recruiting Station Pittsburgh.  During the subsequent three year tour, he was responsible for enlisted and officer procurement from areas in Pennsylvania, New York, Ohio, and West Virginia.

Major Hornfeck returned to the Fleet Marine Forces to serve as the Battalion Executive Officer of 2d Battalion, 7th Marines in July 2020.  He then executed follow-on orders to the MAGTF-TC G-3/5/7 in July 2021, where he was assigned as the Officer-in-Charge of the Service Level Training Division.  In this role, he managed the scheduling and coordination of service-level training exercises, as well as the planning and conduct of the MAGTF Warfighting Exercise.

In June 2023, Lieutenant Colonel Hornfeck reported to 1st Battalion, 7th Marines for duties as the Commanding Officer.