Tilley entered the United States Naval Academy during the height of the Civil War, graduating after the conflict. He gradually rose through the ranks and participated as a lieutenant in the United States military crackdown against strikers in the wake of the Great Railroad Strike of 1877. He and a small contingent of sailors and marines defended the American consulate in Santiago, Chile during the 1891 Chilean Civil War. He was a commander during the Spanish–American War, and his gunship successfully captured two Spanish Navy ships. After the war, he was made the first acting-Governor of Tutuila and Manua (later called American Samoa) and set legal and administrative precedents for the new territory. After 41 years of service, he was promoted to rear admiral but died of pneumonia shortly afterwards.