Gomez studied medicine at the University of Santo Tomas but finished his degree in Madrid, Spain. He joined the group of young and patriotic middle-class Filipinos of intelligence, courage, and prominence led by Dr. Jose Rizal and Marcelo H. del Pilar, the same group who organized the Propaganda Movement to work in Spain for political and social reforms in the Philippines. Under the pseudonym “Ramiro Franco”, he supported the movement through his contributions for the official publication of the organization, La Solidaridad, which he also helped finance from 1889 to 1895.
As the new president of the newly reorganized Union Obrero Democratica de Filipinas, the first labor union in the Philippines, Dominador Gomez encouraged the establishment of cooperatives and medical and legal services for union members. Gomez took over and changed the name of UOD into Union Obrero Democratica de Filipinas (UODF). On May 1, 1903, he led a mass rally of about 100,000 workers who marched from Plaza Moriones in Tondo to Malacañang in protest against the American regime's policy for suppression and calling for political independence, shouting “Down with U.S. Imperialism!” In 1913, the Philippine Legislature officially declared this date as Labor Day. As a consequence of the protest, Gomez was arrested for illegal association and sedition and was tried and sentenced to one year hard labor. Later, he considered himself vindicated with his election as a delegate to the first Philippine Assembly in 1907.
Together with Pedro A. Paterno and Pascual H. Poblete, they organized the Nacionalista Party in 1900 and again in 1901, driven by the group's intention to gain outright autonomy for the Philippines. In later years, he joined the Federo-Tercerista group, also known as the Democratic Progresistas, in the opposition to the powerful Nacionalistas.
In 1916, Gomez became president of the municipal board of Manila, to which he had earlier been elected a member. His first official act was to call the attention of his colleagues to their responsibilities to their constituents.
While the Philippines was still a colony of Spain, Gomez served as a volunteer in the Spanish army in the war in Cuba, and was decorated by Queen Maria Cristina for his bravery.