Rear Adm. Kristin L. McCarthy is a native of San Diego, California. She graduated with a Bachelor of Arts in History from University of California, Los Angeles in 1993, and then earned her Juris Doctor from The University of Southern California Gould School of Law in May 1996. She reported to her first permanent duty station, Pearl Harbor, Hawaii in 1997.

McCarthy served as a defense counsel at Naval Legal Service Office (NLSO) Pacific Detachment-Pearl Harbor, representing Sailors and Marines at courts-martial and administrative hearings throughout the Pacific. Next, she became the Staff Judge Advocate (SJA) at the Pearl Harbor Naval Shipyard and Intermediate Maintenance Facility. Soon after, McCarthy took on additional responsibility as Assistant Force Judge Advocate for the Commander in Chief, U. S. Pacific Fleet. In 1999, she transferred to NLSO North Central as a legal assistance attorney and claims officer. In 2000, she became the Officer in Charge at the Joint Pentagon Legal Assistance Office.

After the birth of her son, McCarthy left active duty, returning to San Diego in 2004. She transitioned to Selected Reserve status in 2005, joining Navy Reserve (NR) Region Legal Service Office (RLSO) Southwest as the Training and Division Officer. In 2007, McCarthy mobilized as the SJA for Naval Coastal Warfare Group ONE and Explosive Ordnance Disposal Group ONE. Upon completion of mobilization orders, McCarthy volunteered to serve as Assistant SJA for Commander, Navy Region Southwest (CNRSW) during a manning crisis.

McCarthy transferred to NR Expeditionary Strike Group (ESG) 3 in 2008. In 2009, she served as Operational Environmental Counsel at RLSO Southwest. From 2009 to 2010, she provided Commander Naval Special Warfare Command support in both the Inspector General and SJA offices. In December 2009, McCarthy was selected as the Executive Officer for NR ESG 3. In 2010 and 2011, while providing legal expertise to both ESG 3 active and reserve, she served as Deputy SJA at CNRSW and SJA for Naval Base San Diego, supervised the RLSO Southwest post-trial process, and provided Freedom of Information Act, military justice, and ethics support to Commander, Naval Air Forces. She received the Rear Admiral Hugh H. Howell, Jr. Award of Excellence (Junior Officer) in 2011.

McCarthy was the Deputy SJA for Reserve Component Command Southwest from 2011 to 2013. During this tour, she received the 2013 Rear Admiral Hugh H. Howell, Jr. Award of Excellence (Senior Officer). She served as Executive Officer for NR RLSO Southwest from 2013 to 2015, and then as Executive Officer for NR Defense Service Office (DSO) West from 2015 to 2017. McCarthy was the Commanding Officer of NR DSO West from 2017 to 2019. From December 2019 to November 2020, she was the SJA for Reserve Component Command Great Lakes and then the SJA for Reserve Component Command Southeast through February 2021. After her second Commanding Officer tour at NR RLSO Southwest ended in February 2023, she became the Director of Legal Services for the JAG Corps Reserve Component through September 2025.

McCarthy is a member of the California bar and is admitted to practice before the courts of the State of California, the U.S. District Court for the Southern District of California, and the U.S. Court of Appeals for the Armed Forces. Her military decorations include the Meritorious Service Medal (five awards), Navy Commendation Medal (five awards), Navy Achievement Medal (two awards), and Navy Unit Commendation Medal.