Sergeant Major John L. Estrada enlisted on 5 September 1973 and attended recruit training at Marine Corps Recruit Depot Parris Island, South Carolina. After completing F-4 aircraft maintenance schools at Naval Air Station (NAS), Memphis Tennessee, and Marine Corps Air Station (MCAS) Cherry Point, North Carolina, PFC Estrada was assigned to Marine Fighter Attack Squadron 451 at MCAS Beaufort, South Carolina, in March 1974.

In December 1974, LCpl Estrada was transferred to Marine Fighter Attack Squadron 232, 1st Marine Aircraft Wing, Iwakuni, Japan. He was meritoriously promoted to corporal in March 1975. In February 1976, Sgt Estrada served with Marine Fighter Attack Training Squadron 101, MCAS Yuma, Arizona. In September 1977, he transferred to Marine Fighter Attack Squadron 314, MCAS El Toro, California. Reassigned to Marine Fighter Attack Squadron 323 in December 1978, he deployed with the squadron in November 1979 for seven months aboard the aircraft carrier USS Coral Sea to the Western Pacific and Arabian Gulf. In June 1980, SSgt Estrada transferred to Marine Reserve Fighter Attack Squadron 321, Marine Aircraft Group 41, Detachment "A" at Andrews Air Force Base, Maryland.

In August 1982, SSgt Estrada was ordered to Drill Instructor duty at Marine Corps Recruit Depot San Diego, California, where he served with Company K, 3d Recruit Training Battalion. He was meritoriously promoted to gunnery sergeant in January 1984. In October 1984, GySgt Estrada returned to MCAS Beaufort for duty with Marine Fighter Attack Squadron 251 as the Noncommissioned Officer in Charge of the Airframes Division. In November 1985, he was reassigned to Marine Fighter Attack Squadron 451 and deployed to the Western Pacific from January to July 1986 under the Unit Deployment Program. From January to March 1987, GySgt Estrada attended aircraft maintenance schools at NAS Cecil Field, Jacksonville, Florida, retraining as an FA-18 Hydraulic/Structural Mechanic.

In October 1987, GySgt Estrada returned to Drill Instructor duty, this time at MCRD Parris Island. He served as Series Chief Drill Instructor with Company I, 3d Recruit Training Battalion and subsequently as Standing Operations Procedures (SOP) Instructor and Drill Master at Drill Instructor School as the SOP Instructor and Drill Master until his promotion to first sergeant in October 1990.

From December 1990 to March 1995, 1stSgt Estrada served as First Sergeant for Intelligence Company, 3d Surveillance Reconnaissance Intelligence Group, Camp Hansen, Okinawa, Japan; Marine Security Force Company, Norfolk, Virginia; Electronics Maintenance Company, 1st Maintenance Battalion, 1st Force Service Support Group, Camp Pendleton, California; and Company A, 1st Light Armored Reconnaissance Battalion, 1st Marine Division, Camp Pendleton.

From March 1995 to May 1998, SgtMaj Estrada served as Sergeant Major for 2d Battalion, 1st Marines, BLT 2/1, 1st Marine Division, Camp Pendleton; and deployed with the 11th Marine Expeditionary Unit (MEU) (Special Operations Capable) (SOC) and 15th MEU (SOC) to the Western Pacific and the Arabian Gulf.

In May 1998, SgtMaj Estrada assumed the duties as Sergeant Major for Recruiting Station Sacramento, California, in the 12th Marine Corps District, Western Recruiting Region. From April 2000 to October 2001, SgtMaj Estrada was assigned as Sergeant Major, Recruit Training Regiment, MCRD Parris Island.

From December 2001 to May 2003, SgtMaj Estrada served as the Sergeant Major, 3d Marine Aircraft Wing. During this assignment, he was forward deployed and participated in Operation Southern Watch, Operation Enduring Freedom, and Operation Iraqi Freedom.

Sergeant Major Estrada assumed the post as the 15th Sergeant Major of the Marine Corps on 26 June 2003 and served in this position until 25 April 2007. He retired from the Marine Corps in June 2007.

His personal awards include the Bronze Star, the Meritorious Service Medal with three gold stars, the Navy and Marine Corps Commendation Medal, the Joint Service Achievement Medal, and the Navy and Marine Corps Achievement Medal.