Gongsun Kang was the son of Gongsun Du, the Administrator of Liaodong. In 204, Gongsun Kang inherited his father's appointment and controlled the territories of Liaodong, Xuantu and Lelang. He was nominally subject to the Han DynastychancellorCao Cao, while keeping his domain semi-independent of the central government. In 207, when Yuan Shang and Yuan Xi fled to Liaodong after being defeated by Cao Cao's forces, Gongsun killed the Yuans and sent their heads to Cao.
Gongsun also defeated Yiyimo, king of Goguryeo, at his capital and forced him to move the capital. He separated the southern half of Lelang Commandery and established Daifang Commandery in 204 to make administration more efficient. He also attacked the southern natives and forced them to submit to the Han Dynasty.
When Gongsun died, his younger brother Gongsun Gong succeeded him because his children were still too young. Gongsun Kang's son Gongsun Yuan took back control of Liaodong in 228.