During Former Qin
Upon Murong Chui's arrival in Former Qin territory, Fu Jiān, who had long considered conquering Former Yan but feared Murong Chui's military ability, was greatly pleased and exited the capital Chang'an to personally welcome Murong Chui. He created Murong Chui the Marquess of Bintu and greatly honored him, despite misgivings by his prime minister Wang Meng. He also made Murong Chui one of his generals.
Later in 369, after Murong Ping refused to cede the Luoyang region to Former Qin, as Former Yan had promised when seeking Former Qin's aid against Jin, Fu Jiān sent Wang to attack Former Yan. Wang requested that Murong Chui's heir apparent Murong Ling accompany him as a guide. After capturing Luoyang in early 370, Wang bribed Murong Chui's attendant Jin Xi (金熙) to give Murong Ling a false message that Murong Chui had heard that Empress Dowager Kezuhun had regretted her actions and that, therefore, he was defecting back to Former Yan. Murong Ling, unable to verify either the truth or the falsehood of the message, decided to defect back to Former Yan. Wang immediately accused Murong Ling of treason, and Murong Chui, in fear, fled, but was captured, although Fu Jiān believed that Murong Ling was acting independently and therefore pardoned Murong Chui. Former Yan did not trust Murong Ling and exiled him, and later that year, after he tried to start a rebellion, he was killed in battle after being betrayed by his brother Murong Lin.
Late in 370, after Wang defeated Murong Ping and conquered Former Yan, Murong Chui accompanied Fu Jiān to visit the Former Yan capital Yecheng. Initially, he did not hide his disgust to those officials who failed to support him during the struggle with Murong Ping and Empress Dowager Kezuhun, but at Gao Bi's suggestion, he started to treat them with kindness, with the rebuilding of Yan in mind. Still, in 372, he accused Murong Ping of being the root of Former Yan's destruction and requested that Fu Jiān avenge Former Yan by executing Murong Ping; Fu Jiān did not do so, but effectively exiled Murong Ping by making him the governor of a distant commandery.
In 378, Murong Chui participated in the campaign commanded by Fu Jiān's son Fu Pi against Jin's key city of Xiangyang. In 382, when Fu Jiān wanted to launch a major campaign to destroy Jin and unite China, most officials, including Fu Jiān's brother Fu Rong, who succeeded Wang as prime minister after Wang's death in 375, opposed, but Murong Chui and Yao Chang urged the campaign, and Fu Jiān launched his campaign in fall 383. However, Former Qin forces, commanded by Fu Rong, was defeated by Jin forces at the Battle of Fei River despite great numerical superiority; Fu Rong was killed, and almost the entire army collapsed—although the forces under Murong Chui's command remained intact, and Fu Jiān, who suffered an arrow wound during the defeat, fled to Murong Chui. Murong Chui's son Murong Bao and brother Murong De both tried to persuade Murong Chui to kill Fu Jiān while he had the power to, but Murong Chui instead returned his forces to Fu Jiān's command and returned to Luoyang with Fu Jiān. However, under suggestion by his son Murong Nong, he planned a rebellion to rebuild Yan.
Murong Chui told Fu Jiān that he was fearful that the people over the Former Yan territory would rebel, and that it would be best if he led a force to pacify the region. Fu Jiān agreed, despite opposition by Quan Yi (權翼). Murong Chui took the army and arrived at Yecheng, which was being defended by Fu Pi. They suspected each other, but each ruled out ambushing the other. When the Dingling chief Zhai Bin (翟斌) rebelled and attacked Luoyang, guarded by Fu Pi's younger brother Fu Hui (苻暉), Fu Pi ordered Murong Chui to put down Zhai's rebellion, and Fu Pi sent his assistant Fu Feilong (苻飛龍) to serve as Murong Chui's assistant. On the way to Luoyang, however, Murong Chui killed Fu Feilong and his Di soldiers and prepared to openly rebel. Meanwhile, despite his suspicions of Murong Chui, Fu Pi did not put Murong Chui's son Murong Nong and nephews Murong Kai and Murong Shao (慕容紹) under surveillance, and the three fled out of Yecheng and started a rebellion of their own.
In spring 384, Murong Chui, not yet in open rebellion against Former Qin, arrived at Luoyang, but Fu Hui, hearing of Fu Feilong's death, refused to welcome him. Murong Chui then entered into an alliance with Zhai Bin, who urged him to take imperial title. Murong Chui refused at this point (reasoning that he should welcome Murong Wei back as emperor) but accepted the title of Prince of Yan, formally breaking away from Former Qin and establishing Later Yan.
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