With his work on the coconut completed, Lava returned to the Philippines in 1934, where he worked as a consulting chemist at Consolidated Mines Inc. in Manila. During this period, he became a member of various academic societies, including the American Chemical Society, the National Research Council of the Philippines, and the American Association for the Advancement of Science. In 1937, he again went to the United States to secure a patent for his coconut process. After successfully patenting it, he returned to the Philippines and set up a pilot plant in 1938. He also discovered other processes to create coconut milk and flour, and experimented with other native products. It was around this time that Vicente Lava joined the Communist Party of the Philippines. The 1930s in the Philippines was a time when agricultural workers and laborers were starting to organize and strike against economic injustices. The Socialist Party, led by Luis Taruc and Pedro Abad Santos, was established in 1929, and the Communist Party, led by Crisanto Evangelista, was founded in 1930. The two parties merged into one Communist Party in 1938. According to Vicente Lava in an unpublished article submitted to Pacific Affairs entitled The Democratic Movement in the Philippines, “together, the merged parties acquired considerable influence among the peasantry of central and southern Luzon and among the workers of Manila and other cities.” After the merger, Lava organized the League For the Defense of Democracy, and was elected a member of the central committee.
In December 1941, as the Japanese struck Pearl Harbor, a simultaneous strike occurred at Clark Air Base in the Philippines. That month, the Communist Party, with the help of Lava, prepared a 12-point memorandum urging national unity and resistance against the Japanese, and pledging loyalty to the Philippines and United States. In February 1942, the leaders of the Communist Party were taken during a Japanese invasion, leaving Vicente Lava as the new general secretary. One month later, in March, the Hukbalahap, an anti-Japanese guerilla force was formed in central Luzon, with Lava as one of its designers. A few months prior to the outbreak of the war, the Japanese offered Lava a sum of ₱1 million for his patented coconut process, but he refused to sell it, believing that it should only be used to advance Philippine industry. In July 1942, the Japanese raided the Lava family home in Bulakan in an attempt to obtain his coconut oil process, as the fuel created by this process could be used in the manufacture of explosives. In 1943, the headquarters of the Hukbalahap in Luzon was raided, and Lava returned to Manila to reorganize the movement from a distance. His proposals were rejected, and he was demoted in the party organization. In 1944, he worked on the organization of a new political party, the Democratic Alliance, and in 1946, he ran for senator for this party, but did not win the election. Beginning in 1944, Lava's health deteriorated. After the war, although he hoped to obtain equipment for his coconut process in the United States, he died of heart disease in Manila on September 16, 1947.