Born on March 27, 1911, in Dagupan, Pangasinan, Liwanag was the sixth of seven children. He entered the Philippine Military Academy at Baguio City in 1933, graduating in the Class of 1938 with a Bachelor of Science degree. The Offshore Patrol, the forerunner of the Philippine Navy, became his posting. When war came, the Offshore Patrol was the only Filipino naval force alongside the United States Asiatic Fleet responsible for the Philippines' naval defense. Liwanag served as supply officer, promoted rapidly through the ranks as the Japanese advance compressed the American and Filipino forces into the Bataan Peninsula. He was there for the fall, and he was there for the liberation of Manila in 1945. Between those two events lay years of war that shaped both a man and a military.

Liwanag volunteered for the Philippine Expeditionary Forces to Korea, the PEFTOK, making him the only Philippine naval officer to join the army's combat contingent. Assigned as a lieutenant commander to the 10th Battalion Combat Team, he served as artillery and logistics officer. The PEFTOK was the first combat unit from Asia to fight alongside United Nations forces in Korea. On April 22, 1951, Liwanag's battalion was deployed five kilometers north of Yeoncheon when the Chinese Spring Offensive struck. Positioned on a hill in the Yultong area, part of the strategic Iron Triangle formed by Chorwon, Kumhwa, and Pyonggang, the 10th BCT faced echelons of night attacks from the Chinese 44th Division. The Filipino battalion held its ground through the night, an action that earned recognition from the United Nations Command.

Rather than returning home after his combat tour, Liwanag extended his service. Reassigned to the Philippine Navy's role in the Korean campaign, he became the senior naval advisor to the Philippine Embassy and liaison officer to United Nations Command Headquarters in Tokyo. He was promoted to Commander in July 1951. Later assignments took him back to Philippine waters. In January 1958, he commanded Operation Bulwark One, the first US-Philippine joint naval exercise since the country's liberation, a harbor defense maneuver designed to test cooperation between the two navies. The exercise involved the Philippine Navy's headquarters, flagship, and multiple supporting vessels alongside US Navy units.

Liwanag's later career revealed a different kind of military challenge. Between 1958 and 1961, President Carlos P. Garcia created the Presidential Enforcement Unit for Southern Philippines to combat rampant customs, revenue, and immigration violations that drained government coffers and undercut legitimate businesses. Liwanag commanded Task Force 10, the naval arm of this effort. The work was neither glamorous nor safe. Smuggling networks in the southern Philippines were entrenched, well-financed, and sometimes violent. Liwanag's task force operated across the maritime corridors between Mindanao and the islands of Southeast Asia, enforcing laws in waters where borders were often theoretical. After 25 years of active service, he retired in December 1963, receiving the Distinguished Service Star.

Liwanag died on April 12, 1967, and was buried at the Libingan ng mga Bayani, the Heroes' Cemetery. His legacy took physical form decades later. On July 7, 2009, the naval station on Thitu Island, the Philippines' most important outpost in the Spratly Islands, was renamed Naval Station Emilio Liwanag -- one of several bases renamed that day to honor distinguished naval officers. Less than a year later, in May 2010 at the 112th Anniversary of the Philippine Navy, a newly commissioned patrol gunboat, PG-118, was christened BRP Emilio Liwanag. The vessel was originally PKM 223, a Chamsuri-class patrol boat from the South Korean Navy, acquired in 2006. The man who fought at Bataan and in Korea now lends his name to a garrison standing watch over one of the most contested stretches of ocean in the world.