Lieutenant General Zilmer was born in Reading, PA. He was commissioned a second lieutenant in the Marine Corps Reserve following his graduation from Kutztown University of Pennsylvania in 1974 where he earned a Bachelor of Science Degree in Secondary Education. Lieutenant General Zilmer also holds a Master of Arts degree in National Security Strategic Studies from the Naval War College.

Following completion of The Basic School, Lieutenant General Zilmer reported to the 3d Marine Division in Okinawa and served as a Rifle Platoon Commander with 3d Battalion, 4th Marines. In June 1976, Lieutenant General Zilmer next reported to the Marine Corps Recruit Depot at Parris Island, SC, where he served as a Series Commander and Company Executive Officer. He reported to the 2d Marine Division in 1980 and served as Assistant Operations Officer and Rifle Company Commander with 2d Battalion, 8th Marines.

In August and September 1982, Lieutenant General Zilmer participated in peacekeeping operations in Beirut, Lebanon. Returning to the United States in November 1982, Lieutenant General Zilmer was next ordered to Marine Barracks, Washington D.C. for assignment and duty with Security Company located at Camp David, MD.

From July 1985 until June 1987, Lieutenant General Zilmer was assigned to The Basic School in Quantico, VA, where he served as Tactics Assistant Group Chief and Company Commander of two student companies. In June 1988, Lieutenant General Zilmer was assigned to the 1st Marine Division, serving initially as Operations Officer and later as Executive Officer of 1st Battalion, 7th Marines and Operations Officer for Task Force Ripper during Operations Desert Shield/Storm in 1990 and 1991.

Following the Gulf War, Lieutenant General Zilmer was reassigned to Headquarters Marine Corps where he served as Section Head of Ground Officer Assignments. In 1993, Lieutenant General Zilmer was again assigned to 1st Marine Division as Commanding Officer of 1st Battalion, 1st Marines and subsequently deployed to Okinawa, Japan as the Ground Combat Element of the 31st Marine Expeditionary Unit (Special Operations Capable). Following a brief assignment as Executive Officer of 1st Marines, Lieutenant General Zilmer was next assigned in 1995 to the Joint Warfare Staff in Poole, England where he served as the Senior U.S. Marine Exchange Officer to the Royal Marines. In July 1997, Lieutenant General Zilmer reported to I Marine Expeditionary Force for duty as Commanding Officer, 15th MEU (SOC). In July 2000, Lieutenant General Zilmer was next assigned to the United States European Command in Stuttgart, Germany where he served as the Deputy Director of Operations and the Director, Counter Terrorism Joint Planning Group. In June 2002, Lieutenant General Zilmer was assigned as Director, Strategy and Plans Division, Plans, Policies and Operations Department at Headquarters, U.S. Marine Corps, Washington, D.C. In June of 2004, Lieutenant General Zilmer was assigned to Marine Corps Base Twentynine Palms, California where he commanded the Marine Air Ground Task Force Training Command.

From September 2005 through June 2007, Lieutenant General Zilmer served as the Commanding General of the 1st Marine Expeditionary Brigade at Camp Pendleton, California. During this time, he also served as the Commanding General of Multi-National Force - West in Al Anbar Province, Iraq in support of Operation Iraqi Freedom.

Lieutenant General Zilmer was appointed to his present rank and assumed duties as Commanding General, III Marine Expeditionary Force; and Commander, Marine Corps Bases Japan from June 2007 through Sept 2009. Upon his departure from Japan, Lieutenant General Zilmer assumed the duties as Deputy Commandant, Manpower and Reserve Affairs, Quantico, VA.

Lieutenant General Zilmer has attended the Infantry Officers Advanced Course at Fort Benning, GA, the Marine Corps Command and Staff Course at Quantico, VA, and the Naval War College in Newport, RI.. LtGen Zilmer is authorized to retain and wear the foreign personal decorations, "Order of National Security Merit Gukseon Medal," conferred by the President of the Republic of Korea, and the "Order of the Rising Sun, Gold and Silver Star," conferred by the Emperor of Japan.