Kirby grew up in St. Petersburg, Florida. He is a 1981 graduate of Saint Petersburg Catholic High School, and a 1985 graduate of the University of South Florida in Tampa, Florida, where he earned a bachelor of arts degree in history. He holds a master of science degree in international relations from Troy University and a master of arts in national security and strategic studies from the Naval War College.
Kirby was commissioned in September 1986 after completing Officer Candidate School at Naval Station Newport, Rhode Island. He qualified as a Surface Warfare Officer aboard the guided-missile frigate USS Aubrey Fitch (FFG 34) before obtaining a lateral transfer to the Restricted Line as a Public Affairs Officer (PAO). As a public affairs officer, Kirby served at sea aboard the aircraft carrier USS Forrestal (CV 59) and on the staff of the Commander, U.S. 2nd Fleet, embarked aboard the command and control ship USS Mount Whitney (LCC 20).
While ashore, Kirby completed tours as an instructor at the U.S. Naval Academy; public affairs officer with the Navy Flight Demonstration Squadron (Blue Angels); editor in chief of the Navy's flagship monthly magazine, All Hands; the staffs of the Chief of Naval Personnel, Commander of U.S. Naval Forces Europe, Chief of Naval Operations, and the special assistant for public affairs to the Chairman of the Joint Chiefs of Staff. His most recent assignment was serving as the deputy assistant secretary of defense for media operations.
Kirby served as the U.S. Navy's chief of information, serving as the principal spokesman for the Department of the Navy and providing strategic communication counsel to the Secretary of the Navy and the Chief of Naval Operations. As the Navy's Chief of Information (CHINFO), he led the Navy's public affairs community consisting of more than 2,700 active and reserve officer, enlisted, and civilian communication professionals. In December 2013, he was appointed by SECDEF Chuck Hagel to be the Pentagon press secretary.
On April 22, 2015, it was announced that Kirby would be the new spokesman for the United States Department of State after he retired from the military later in the year. Admiral Kirby officially became spokesman for the State Department on May 12, 2015.
On December 13, 2016, Kirby said in response to questions from RT correspondent Gayane Chichakyan in a daily press briefing that he has no expectation of being invited by President-elect of the United States Donald Trump to stay on under the leadership of Secretary of State-designate Rex Tillerson and he has "every expectation of resigning at the end of" the Obama Administration. He left office following the inauguration of President Trump on January 20, 2017.
Admiral Kirby has been awarded the Navy Distinguished Service Medal, Defense Superior Service Medal, Legion of Merit, Meritorious Service Medal (four awards), Joint Service Commendation Medal, Navy and Marine Corps Commendation Medal (four awards), and Navy and Marine Corps Achievement Medal, as well as various campaign and service awards.