Murong De was born in 336 to Murong Huang and his concubine Consort Gongsun, who had previously given birth to his older brother Murong Na (慕容納). At that time, Murong Huang was the Duke of Liaodong and a vassal of Jin, although in 337 he claimed for himself the title of Prince of Yan (as Prince Wenming). As this was without Jin authorization (although Emperor Cheng of Jin would retroactively recognize this in 341 by creating him that title), this generally was considered the founding of the independent Former Yan state. When he was young, he was regarded as studious, handsome, and talented.