Such a man was well suited for military service, and Choi quickly gained the confidence of both his men and his king during numerous battles with Japanese pirates who began raiding the Korean coast around 1350.
At 36 years of age he became a national hero when he successfully put down a rebellion by Cho, Il-Shin after his insurgents had surrounded the palace and killed many officials and he had proclaimed himself king. Then, in 1355, an armed rebellion took place in the troubled Mongol Yuan Dynasty that occupied part of China. Choi Yong was sent to help the Mongols quash the rebellion, and his success in nearly thirty different battles won him even more fame and favour at home. Upon returning to Korea, he dutifully reported to King Gongmin the internal problems experienced by the dying Yuan Dynasty, which gave the king the idea that the time was right to reclaim some of the northern territories previously lost to the Mongols. Choi fought to recover various towns west of the Yalu River, to the great delight of his king.
He served briefly as the Mayor of Pyongyang, where his efforts at increasing crop production and mitigating famine won him even more attention as a national hero. Then, in 1363, he distinguished himself further when a powerful government official named Kim, Yon-An tried to take control of the government and Choi was forced to defeat a 10,000-man Mongol force that attacked Goryeo in support of the rebellion.
Meanwhile, following a dream that he thought predicted that a Buddhist monk would save his life, King Gongmin promoted a monk named Shin Ton to a lofty position within his court, and allowed him considerable influence. Shin Ton , though, was ruthless and corrupt, and Choi – who vigorously opposed corruption in the kingdom – found himself at odds with him. Shin Ton engineered false accusations of misconduct against Choi that resulted in a punishment of six years in exile, and brought him dangerously close to the death penalty. When Shin Ton died, though, Choi Yong was restored to his previous position and was immediately asked to prepare a fleet to fight the Japanese pirates and eliminate the remaining Mongol forces on Cheju Island. He engaged the Mongols first, who fought tenaciously, but Choi's forces eventually freed the island. Then, in 1376, the Japanese pirates advanced into Goryeo and captured the city of Kongju. Chong, Mong-Chu secured assistance from the Japanese Shogun to eliminate these pirates, but the Japanese were of little help and General Choi Yong and his subordinate Yi Seonggye managed to rout and eventually defeat them, and reclaim Kongju.
The Ming Dynasty in China had become powerful during the 14th Century, and had driven back the Mongols and occupied part of north-eastern Goryeo. In 1388, General Yi Seonggye was ordered to use his armies to push the Ming armies out of the Korean peninsula. Knowing of the support he enjoyed both from high-ranking government officials and the general populace, however, he decided to return to the capital, Kaesong, and secure control of the government instead of possibly destroying his army by attacking the Chinese. When Yi returned Choi Yong put up a gallant fight at the palace, but was overwhelmed. Records differ as to what happened next, although it seems likely that he was banished to Koyang and later beheaded.
Choi Yong is remembered as a great general who was wholeheartedly devoted to the protection of his country. He risked his life many times for Goryeo, and his unswerving loyalty eventually cost him his life.