He first attained prominence in the Philippine arts scene in the 1960s with a distinct style that fused influences from cubism, surrealism and expressionism. Some classified his style as "figurative expressionism", others merely called it ugly. What could not be doubted was the violence in his imagery, a factor that slighted the commercial viability of his works until the 1980s. He favored such subjects as fighting cocks, rabid dogs, and people enraptured by rage or bound in chains. He painted multiple depictions of the crucified Christ that did not shirk from portraying the agonies normally associated with the crucifixion. When asked why he was so angry, he replied, "Why not? Open your eyes. Look around you. So much anger, sorrow, ugliness. And also madness." The intensity of his works stood in contrast to his own personality, described as "placid and affable".
It did not escape attention that many of Ang Kiukok's most violent or gruesome imagery was painted during the martial law rule of Ferdinand Marcos, though he did not build a reputation for himself as a prominent critic of the Marcos regime. In 2001, President Gloria Macapagal-Arroyo named him a National Artist for Visual Arts.
In the end, Ang Kiukok emerged not only as a critical favorite, but a commercially popular artist as well. Upon his death from cancer on May 9, 2005, it was reported that he and fellow National Artist Fernando Amorsolo were the most widely bidded after Filipino painters in auctions.