In 1978, General Quinlan flew the UH-1 with HML-771until accepting an appointment as an FBI Special Agent in December 1978, assigned to the Los Angeles Division where his duties included direct and undercover investigations of white collar crime, public corruption and organized crime. He served also as an FBI pilot, providing tactical observation and SWAT insertion support during espionage, kidnapping and extortion cases. During this period, General Quinlan served with Mobilization Training Unit (LAW) CA-14 at MCAS El Toro.

In 1982, General Quinlan entered the private practice of law in Newport Beach, California and returned to flying with HMM-764. From 1982-1990, he served in MAG-46, MCAS El Toro, variously as the squadron Operations Officer for amphibious operations aboard the USS Nassau, as MALS-46 Executive Officer, Group Assistant Operations Officer, Intelligence Officer and Director of the SNCO Academy. In 1988, he was assigned to Camp Pendleton as Executive Officer for the stand-up of HMA-775 and as Acting Commanding Officer for Combined Arms Exercise 7-90. In 1990, he returned to MAG-46, El Toro, California, as Mobilization Coordinator and then Group Operations Officer until he took command of HMM-764 in 1993. During this period, HMM-764 received the Chief of Naval Operations Safety Award, the Fourth Marine Aircraft Wing Ensign Pierce Award as most effective operational helicopter squadron and a Joint Meritorious Unit Commendation for Counter-Drug Operations in support of JTF-6.

In 1994, General Quinlan was assigned to the Fourth Marine Aircraft Wing as Combat Readiness Evaluation Officer during Operation Pinnacle Advance and then as Deputy Commander of Marine Air Group-46, where duties included commanding the Aviation Combat Element for Amphibious Operations Training Exercise Summer Thunder-95 and Enhanced Combined Arms Exercise 7-96 with the Royal Marine 45 Commando Group and the 24th Marine Regiment.

In 1996, General Quinlan was assigned to Joint Forces Air Combat Coordinator duties with the Fourth Marine Aircraft Wing. He was selected for promotion to Brigadier General and ordered to Joint Service duty with the United States Transportation Command, Scott Air Force Base, Illinois, as Deputy Director, Plans and Policies (J-5). He was ordered to assume his previous duties as Commanding General, I Marine Expeditionary Force (Augmentation) Command Element (I MACE), Camp Pendleton, California, as well as Deputy Commanding General (Mobilization) I Marine Expeditionary Force on May 15, 1998. He retired after serving as Vice Commander, U.S. Marine Corps Forces Pacific, but was called back to active duty in 2008.

General Quinlan earned a Juris Doctorate from Southwestern University, Los Angeles and a Master of Laws (in taxation) from Boston University. He is the founding partner of Kester & Quinlan, L.L.P, admitted to practice law in California and Colorado, is a member of the Board of Trustees of the Marine Corps University Foundation, the University of California-Irvine School of Social Ecology Associates, the Attorney-Client Relations Committee of Orange County, the California Bar Association and the Corona Del Mar, California, High School Foundation.

In addition to Naval Justice School, General Quinlan attended Amphibious Warfare School, Command and Staff College, Landing Force Staff Planning, Reserve Components National Security Course, the Senior Officer Course of the Army War College and the Capstone Course of The National Defense University.

General Quinlan's decorations include the Defense Meritorious Service Medal, Meritorious Service Medal, Joint Meritorious Unit Commendation, Meritorious Unit Commendation, National Defense Service Medal with bronze star, Sea Service Deployment Ribbon, Armed Forces Reserve Medal (2d award) and Marine Corps Reserve Medal with three bronze stars.