[2][3] Upon graduation, Velasco joined the faculty of the University of the Philippines and remained there for the duration of World War II, during which he endured a brief period of incarceration by the Japanese army.

[4] After the war, Velasco pursued graduate studies in the United States and obtained a Ph.D in plant physiology from the University of California, Berkeley in 1949.

Among his findings, which were published only after the end of the war, was that the Elon-elon variety flowered during short days when there was less than 12 hours of light.

[6] With respect to cadang-cadang, Velasco was skeptical of the still-prevalent view that the disease was viral in nature, and devoted considerable effort to prove his thesis that it was caused by an element in the soil that was toxic to the coconut plant.

[6][3] In 1967, Velasco was appointed Commissioner of the National Institute of Science and Technology, a position he held for 10 years.