His brother Pedro eventually emerged as a leading socialist leader during the Commonwealth era.

He was admitted to the Philippine Bar and passed in 1911 and later served as assistant attorney at the Bureau of Justice from 1913 to 1917.

Abad Santos then served as chief counsel of the president of the Senate and the speaker of the House of Representatives of the Philippines.

Abad Santos accompanied the Commonwealth government to Corregidor, where on December 30, 1941, he administered the oath of office to President Quezon and Vice-President Osmeña for the second term to which they had been elected in November of that year.

He also undertook, with Manuel Roxas, the supervision of the destruction of Commonwealth government currency to prevent its falling into enemy hands.

With the Japanese invasion rapidly advancing to the southern part of the Philippines, President Manuel L. Quezon was advised by General Douglas MacArthur to establish a government in exile to the United States; Quezon invited Chief Justice Abad Santos to leave with him.

Although he had nothing to do with military operations, they imputed to him, as acting president, the destruction of the bridges and other public works in Cebu that had been undertaken by the USAFFE forces to delay the invasion of the island.

The Japanese high commander, Kiyotake Kawaguchi, took him and his son aboard a ship on April 26, 1942, thinking they were heading to Manila.

After two days' confinement at Japanese camps, Abad Santos was called in front of Kawaguchi and was informed about the order of his execution.

Abad Santos was executed at 2:00 pm, on May 1, 1942, under a tall coconut tree near a river bank.

[1] On May 1, 1942, Chief Justice Jose Abad Santos was executed by Japanese troops in Malabang, Lanao del Sur.