Born and raised in San Mateo, California, Major General Simcock was commissioned a Second Lieutenant in May 1983 via the PLC Program. Following graduation from The Marine Officer Basic School and the Infantry Officer Course in Quantico, Virginia, he was assigned to 2d Battalion, 3d Marines, 1st Marine Brigade, Kaneohe, Hawaii. There he served with Fox Company as a Rifle Platoon Commander, Executive Officer, and Company Commander.
In July 1987, First Lieutenant Simcock was assigned to the 3d Recruit Training Battalion, Recruit Training Regiment, Marine Corps Recruit Depot, San Diego, California. While on the drill field, he served with various training companies as an Assistant Series Commander, Series Commander, and Company Commander. During his tour in San Diego, First Lieutenant Simcock was promoted to Captain and selected to attend the Amphibious Warfare School in Quantico, Virginia. In August 1991, Captain Simcock reported to 3rd Battalion, 5th Marines, 1st Marine Division, Camp Pendleton, California. There he served as the Assistant Operations Officer and Commanding Officer of India Company 3/5.
Upon completion of his tour with 3/5 in August 1993, Captain Simcock was assigned to Inspector-Instructor duty with the 25th Marine Regiment in Worcester, Massachusetts. There he served as the Regimental Operations Officer. Following promotion to Major and completion of I-I duty, he attended the U.S. Marine Corps Command and Staff College.
In July 1996, Major Simcock reported to Tampa, Florida for a Joint assignment at Special Operations Command Central where he served in the J-5, Plans and Policy Directorate as the Chief of Plans. In June 1999, Major Simcock was ordered overseas to Okinawa, Japan where he served as the G-3 Future Operations Officer for III MEF and was promoted to Lieutenant Colonel. In June 2000, Lieutenant Colonel Simcock returned to CONUS and was assigned to the Marine Corps Air Ground Combat Center at 29 Palms, California where he assumed command of 1st Battalion, 7th Marines on 11 August 2000.
Following Battalion Command in August 2002, Lieutenant Colonel Simcock was selected to attend Top Level School at the Naval War College in Newport, Rhode Island. After graduation in November 2003, he reported to Headquarters U.S. Marine Corps for duty as the Congressional Liaison Officer to the U.S. House of Representatives where he was promoted to Colonel. He detached from this assignment in May 2006 and assumed command of the 6th Marine Regiment in June 2006. Colonel Simcock relinquished command of 6th Marines in May 2008 and transferred to the MAGTF Training Center, 29 Palms, California where he served as the Director of the Tactical Training and Exercise Control Group. Selected to Brigadier General, he transferred in August 2009 to Headquarters U.S. Marine Corps serving as the Legislative Assistant to the Commandant. In June 2012, Brigadier General Simcock served in OSD, Asia and Pacific Affairs as the Principal Director, South and South East Asia.
Major General Simcock was promoted to his current rank on April 1, 2014 and is currently serving as the Deputy Commander for U.S. Marine Forces, Pacific.