He Graduated from the University of Santo Tomas College of Medicine in 1916. He started his career as a military surgeon shortly after his graduation by joining French Red Cross, later the American Red Cross during World War I. After the war, he became a Red Cross Commissioner and was assigned to various countries. In 1919, he was forced to return to Manila due to illness. He briefly went to private practice and teaching but joined government as First Lieutenant and medical Inspector in the Philippine Constabulary in 1921. He rose to become Lieutenant Colonel and Chief Surgeon in 1926 and became the first Commissioner of Health and Public Welfare in 1932. In 1934, he became Brigadier General Chief of Staff of the Philippine Constabulary. In 1936, he became Major General and Deputy Chief of Staff of the Philippine Army. When the Constabulary separated from the army in 19 38, Gen. Valdez became the PC Chief. He was instrumental in obtaining the land where Camp Crame and Camp Aguinaldo are now located. In 1939, Gen. Valdez was re-appointed Chief of Staff of the Philippine Army. In 1941, while the seat of the Commonwealth government he was also appointed as Secretary of National Defense. Since he was also President Quezon’s attending physician, he was forced to join the Commonwealth cabinet in exile in the USA where he helped lobby for Philippine independence.

In 1944, President Osmeña re-established Commonwealth government in Tacloban, Leyte in February 1945, appointed Gen. Valdez as Secretary of Health, in addition to his duties as Secretary of Defense and Chief of Staff of the Philippine Army. As Secretary of Health and National Defense, he organized the services of the Philippine Civil Affairs Unit (PCAU) which brought in food, medicines, vitamins and other supplies from the US Medical Corps. His Red Cross training in the past was quite useful to him all throughout the war. The PCAU organized food distribution centers in Manila and the Province. He relinquished his post as Defense Secretary in April 1945. He retired for government service as Chief of Staff of the Philippine Army when President Roxas took his oath of office in July 4, 1946. He went back from teaching jobs and private practice and help establish the Lourdes Hospital in 1950.