He was captured during the Filipino-American War in July 1900. After his release, he joined the Federal Party and was appointed as provincial fiscal of Albay on 13 May 1901 (until 1905). In 1904, he was part of the honorary board of Filipino commissioners who took part in the Louisiana Purchase Exposition under Dr. Trinidad Pardo de Tavera. Calleja received a gold medal of honour during the said exposition.