In 354, after Murong De's older brother Murong Jun (Emperor Jingzhao) formally broke from Jin and claimed imperial title, he created Murong De the Duke of Liang. Sometime after Murong Jun died in 360 and was succeeded by his son Murong Wei, Murong De was created the Prince of Fanyang. By 368, he was the mayor of the capital Yecheng (鄴城, in modern Handan, Hebei) when four dukes of the rival Former Qin rebelled against Former Qin's emperor Fu Jiān. Murong De suggested to the regent, his uncle Murong Ping, that Former Yan activate its troops to aid one of them, Fu Sou (苻廋) the Duke of Wei and further take the chance to conquer Former Qin, but his strategy was rejected by Murong Ping.