He became emperor at age 10 and, late in his reign, with powers in the hands of his mother Empress Dowager Kezuhun and his incompetent and corrupt granduncle Murong Ping, was captured by Former Qin's prime minister Wang Meng in 370, ending Former Yan.
In 359, at an imperial feast, Murong Jun remembered Crown Prince Ye and was weeping.
Empress Dowager Kezuhun believed him, but Murong Wei did not and refused to authorize his actions.
Murong Ke was an able regent in both governance and military matters, and Former Yan's territorial expansion continued gradually during his regency, largely at Jin's expense.
Upon hearing about Murong Ke's death, the rival Former Qin's emperor Fu Jiān began considering plans to conquer Former Yan.
As Fu Sou held the important gateway city of Shancheng (陝城, in modern Sanmenxia, Henan), this opened up the center of Former Qin to Former Yan.
However, Murong Ping refused to act, and in late 368, Fu Jiān defeated the four rebel dukes.
In 369, probably at his mother's instigation, Murong Wei married the daughter of her cousin Kezuhun Yi (可足渾翼) as his empress.
Murong Chui, hearing the news, fled to Former Qin and became a general for Fu Jiān.
In anger, late in 369, Fu Jian sent a 60,000-men force, commanded by his prime minister Wang Meng, against Former Yan.
He then advanced on Hu Pass (壺關, in modern Changzhi, Shanxi), defeating all Former Yan resistance on the way.
Meanwhile, Murong Ping made the worst display of his corruption at this time—keeping guards at forests and streams, disallowing commoners and even his own soldiers from cutting firewood or fishing unless they paid a usage fee in either money or silk.
Murong Wei, hearing this, sent a messenger to rebuke him and ordering him to distribute the wealth to the soldiers, but the damage was done.
Murong Wei, along with his brothers, abandoned Yecheng, intended to flee back to Helong.
He put Chang'an under a siege and demanded that Fu Jiān deliver Murong Wei to him.
Fu Jiān agreed to attend, but could not go due to rain, and news of the conspiracy leaked.