Manuel L. Quezon became the first President of the Commonwealth and Harrison was asked to be Quezon's principal advisor in November 1935. He served in that capacity for ten months. In 1936, Harrison expressed interest in acquiring Filipino citizenship but did not fulfill the required years of residency under the Naturalization Law. Upon Manuel Quezon's initiative, the National Assembly passed Commonwealth Act No. 79, making him a naturalized Filipino citizen. Harrison returned to the position of advisor upon Quezon's request in May 1942, after Filipino and American troops had surrendered the Bataan Peninsula and Corregidor Island during World War II and Quezon went into exile in the United States. Harrison would serve the government-in-exile.