Even during the pre-war years. Ka Amado, as he was fondly called, was already a well-known journalist. From being a reporter for the morning daily, Watawat, he became the star columnist of Pagkakaisa and thereafter the editor of Mabuhay. Coupled with these responsibilities he pursued his literary career. His poems and stories were included in such anthologies as Clodualdo del Mundo's Parolang Ginto and Alejandro Abadilla's Talaang Bughaw.

He was the vice-president of the "Aklatang Bayan," one of the Philippines' first writers' societies, where he met the great names of Tagalog literature including Lope K. Santos. Upon the establishment of "Ilaw at Panitik" in 1922, he became a member and rubbed shoulders with the great Tagalog lyricist, Jose Corazon de Jesus, then the idol of his generation. In 1924, Hernandez was honored as Filipino poet laureate.

In June 1932 he married Atang de la Rama, the great queen of Tagalog song and star of the zarzuela, by whom he had a son, Rene, their only child.

When the Japanese invaded the Philippines, Amado joined the resistance movement and became an intelligence operative of the Marking and Anderson guerrilla outfit whose operations covered Hagonoy, Bulacan, and the mountain fastnesses of the Sierra Madre.

After the war, he was back in Manila, and became a labor leader.

He was appointed councilor of Manila by President Sergio Osmeña. At the same time, he became president of the Philippine Newspaper Guild. From literature, his interest shifted to mass movements.

On May 5, 1947, he led the biggest strike ever to hit Manila. He was then an officer of the biggest and most powerful federation of labor unions in the Philippines - the Congress of Labor Organizations (CLO).

The following month, he became the president of this organization. Much later, he became a member of the party, which had been organized under the guidance of the Communist Party of the Philippines. This turn of events was brought about by his war experience and by the fact that those who led the movement were his friends. More important though was the pressure of events, which triggered the seeking of freedom through one way-revolution. On May 1, 1948, as president of the CLO, Ka Amado led a huge demonstration in Manila. After this, he left for the United States and Europe to gather more knowledge on the international working-class movement.

In 1950, the entire political bureau of the Communist Party of the Philippines was rounded up by the military. The headquarters of the CLO was raided on January 20, 1951. On the 26th, Hernandez was "invited" to Camp Murphy. It was the beginning of his ordeal. For six months he was clandestinely transferred from one military camp to another, to the anguish of both his family and his friends. After nearly half a year of imprisonment, he was finally charged with rebellion complexed with murder, arson and robbery. The main charge against him was that he had given a mimeograph machine to the Huks.

For six years he was incarcerated in five different prisons - Camp Murphy, Camp Crame, Muntinglupa, Fort MacKinley and the Panopio Compound. During his trial he was assisted by legal luminaries like Claro M. Recto, Jose P. Laurel and Claudio Teehankee. When he was sentenced to life imprisonment, he appealed his case to the Supreme Court, While his appeal was pending, he stayed behind bars with other convicts accused of various political crimes.

In prison he did not develop the paralyzing bitterness that afflicts ordinary inmates. He continued writing and from those years came Isang Dipang Langit, a poignant testimony of human endurance and constancy. This collection was translated into English as Rice Grains and Other Poems, by E. San Juan, Jr. It was also translated into Russian. Isang Dipang Langit won for him the Republic Cultural Heritage Award. Bayang Malaya was also written while he was in prison. It later won for him the first Balagtas Award sponsored by the First Couple. Considered his masterpiece is Luha ng Buwaya, written in prison with the easy style of contemporary Pilipino. Portions of the novel, Mga Ibong Mandaragit were also started while he was behind bars. Moreover, he edited the Muntinglupa Courier, a small prison newspaper.

On June 20, 1956, he was given temporary freedom under bail by the Supreme Court. On May 1, 1964, the same tribunal acquitted him.

Upon his release, he went back to writing and lecturing. He became a columnist of Taliba. Despite the passage of time and the changes in political climate, he remained a social critic.
In 1966, he was in the People's Republic of China to attend the Afro-Asian Writers emergency conference held in Yenan province. He also participated in the War Crimes Tribunal on American crimes in Vietnam, where he defended the Philippines from charges that it was "a criminal country for sending the PHILCAG to Vietnam."

He was teaching at the U.P when he died on March 24, 1970. The two-time awardee in the Commonwealth Literary Contest; four-time winner of the Palanca Literary Memorial Awards; winner of four consecutive years of journalism awards in the NPC-ESSO sponsored contest, editor of four papers in the vernacular; and the first Filipino "King of Balagtasan" finally succumbed to rest for eternity.
University of the Philippines posthumously conferred on him the title of Doctor of Humanities, honoris causa. The Ateneo de Manila University awarded him its "Tanglaw ng Lahi" award.