This would have given him a very high position in the Silla bone rank system, which governed the political and military status that a person could attain.

Kim Yu-sin's first military engagement in command is believed to have occurred around 629 AD, and through it he quickly proved his capabilities as a warrior.

It was during this period that Yu-sin rose through the ranks of the military, rising to the position of general and becoming a skilled field commander.

Eventually, with the help of a 50,000 man Silla army and some 130,000 Tang forces, Yushin attacked the Baekje capital, Sabi, in 660, in the Battle of Hwangsanbeol.

One legend states that Kim was once ordered to subdue a rebel army, but his troops refused to fight as they had seen a large star fall from the sky and took this to be a bad omen.

Other legends mention how General Kim ingeniously used kites as a means of communication between his troops when they had become divided between islands and the mainland.

In 668, King Munmu bestowed upon him the honorary title of Taedaegakgan (태대각간; 太大角干), something like "Supreme Herald of Defense" (literally "greatest-great-trumpet-shield").

Following his death on 21 August (the 1st day of the 7th lunar month) 673, General Kim was awarded the honorary title of King Heungmu.

Kim Yu-sin's third wife, Lady Jiso (Hanja:智炤夫人), was the third daughter of King Muyeol of Silla.

His second son, Kim Won-sul, would later play a central role in completing the independence of Silla from the Tang dynasty.

One of his ten children, his second son Kim Won-sul, became a general during the reign of King Munmu and was essential in unifying Silla.