He passed the Korean national military examinations at the age of 22. Sin earned prominence by driving out the Nitanggae barbarians from the northern provinces of Joseon dynasty. Sin was a successful general who also gained renown for protecting the borders of Joseon against the Jurchen. When the fortifications at Busan fell to the Japanese at the outset of the Japanese invasions of Korea (1592–1598), Sin Rip, the Vice Minister of War, was despatched to Chungju to stop the advancing invaders. He raised a substantial force, 8,000 strong, consisting primarily of cavalry. He was joined at Chungju by Gyeongsang Provincial Governor Kim Su, who had previously collected a large force at Daegu while waiting for a general to be sent from the capital, Hanseong (modern day Seoul). When no general materialized and it was learned that the Japanese were en route, Kim's force largely evaporated.