Alcheon supported Princess Deokman in politics and in her succession to the throne after the death of her father, Jinpyeong of Silla. It was with Kim Alcheon's support that Princess Deokman became Queen Seondeok of Silla.
He was a notable general during the Seondeok era. In 636, he obeyed the order of the queen and marched to Yeoguen-gok (女根谷) and then repulsed the Baekje forces. In 638, Goguryeo forces invaded Chiljung castle (today's Paju). Alcheon led his soldiers to victory over the Goguryeo forces.
In 647, Alcheon was promoted to Sangdaedeung. It is likely that he was elevated by Queen Jindeok, the successor of Queen Seondeok, who died in February of that year, although it is possible that Seondeok had promoted him before her death.
In 654, Queen Jindeok died without a successor, Alcheon became the favorite to take the throne of Silla. However, Alcheon refused to take the crown and, along with Kim Yushin, supported Kim Chunchu. As a result, Kim Chunchu ascended the throne as King Muyeol.
- ^ Il-yeon: Samguk Yusa: Legends and History of the Three Kingdoms of Ancient Korea, translated by Tae-Hung Ha and Grafton K. Mintz. Book One, page 64. Silk Pagoda (2006). ISBN 1-59654-348-5