Sometime before 345, he was given the important defense post of Liaodong (遼東, in modern Liaoyang, Liaoning) with the responsibility of defending the eastern border against Goguryeo.
In 350, Former Yan forces quickly captured Later Zhao's You Province (幽州, modern Beijing, Tianjin, and northern Hebei).
Murong Ke's military discipline was said to be so strict that not even trees and grass were harmed as his army marched through a region, and he quickly seized a number of commanderies in Ji Province (冀州, modern central Hebei) from Ran Wei, the new state established by Shi Min (who had by now changed his name to Ran Min, back to the family name that his father had before he was adopted by Shi Hu).
Murong Ke pretended to repeatedly lose engagements, and Ran Wei forces were drawn into the plains.
These included campaigns against Su Lin (蘇林) in winter 352, Li Du (李犢) in summer 353, and Lü Hu (呂護) in spring 354.
In 356, Murong Ke further defeated Duan Kan (段龕), the Jin vassal who had occupied Shandong Peninsula under the title Duke of Qi, sieging his heavily fortified capital Guanggu (廣固, in modern Qingzhou, Shandong) and forcing his surrender.
As far as his military command style was concerned, this was said about it in Sima Guang's Zizhi Tongjian: Indeed, in recorded history there was not a single mention that Murong Ke lost a battle.
In 365, after a fierce attack, Luoyang fell, and he captured the Jin general Shen Jing (沈勁), whom he initially wanted to spare, but who continuously refused to submit and therefore whom his deputy Muyu Qian (慕輿虔) insisted on executing.
Murong Ke, upon return to Yecheng, stated that he felt ashamed that he was unable to preserve Shen's life and allow his abilities to be used by Former Yan.
(As Former Qin's capable prime minister Wang Meng approached the Former Yan capital Yecheng, his army showed the same discipline that Murong Ke's did, and the people joyously stated, "We have met the Prince of Taiyuan again!"