He, along with Murong Wei's mother Empress Dowager Kezuhun, is often blamed for the Former Yan's decline and fall.
(This is corroborated in that his grandnephew Murong Wei, at one point, referred to him as an uncle rather than a granduncle, perhaps out of confusion in his young age.)
The first reference to him in history was in 339, when he was mentioned as one of Murong Huang's generals (along with another brother, Murong Jun (慕容軍, note different tone and character than his nephew who would later inherit the throne), Muyu Gen, and Muyu Ni (慕輿泥)) who conducted a successful raid against Later Zhao's border region.
In Murong Jun's campaigns over the next few years, which saw him seize much of Later Zhao's territory and capture Shi Min (who had by then changed him name to Ran Min, to the family name that his father had before his adoption by Shi Hu) and destroy his short-lived state Ran Wei, Murong Ping served as a major general.
Over the next few years, Murong Ping would be involved in leading armies against various former Later Zhao generals who were still trying to maintain independence and vacillating between Former Yan, Former Qin, and Jin.
Empress Dowager Kezuhun believed Muyu, but the young emperor did not and refused to authorize his actions.
His regency was considered a successful one, as he governed the empire with efficiency while expanding its borders southward, at Jin's expense.
Murong Ping himself assumed the regency and held power in conjunction with Empress Dowager Kezuhun.
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.