Due to the turmoil in northern China, Gu Rong returned to his hometown in the Jiangnan, where, despite initially joining, he played a decisive role in quelling Chen Min's rebellion in 307.
In his final years, he served the Prince of Langya and future founding emperor of the Eastern Jin, Sima Rui, helping him lay the foundations for the dynasty in the south.
Gu Rong also served the Eastern Wu at a young age, and was appointed as a Gentleman of the Yellow Gate and Commandant Who Upholds Righteousness to the Crown Prince.
Gu Rong spent his days drinking and ignoring his official duties before telling his friend, Feng Xiong (馮熊) about the matter.
Feng Xiong therefore persuaded Jiong's chief clerk, Ge Yu (葛旟) to transfer Gu Rong to the office of Palace Secretarial Attendant.
Gu Rong sided with Ai and defeated Ge Yu, so he was conferred the title of Earl of Xixing and transferred to the office of Internal Companion of the Crown Prince.
However, along the way, Luoyang was occupied by Zhang Fang, a general of the Prince of Hejian, Sima Yong, and Gu Rong was unable to proceed, so he fled to Chenliu.
Gu Rong and many of the local gentry clans initially recognized his rule, and he served as General of the Right and Interior Minister of Danyang under Chen Min.
They secretly informed the Jin general, Liu Zhun (劉準) in Shouchun regarding their plot and asked him to send his soldiers south of the Yangzi while they acted from within.
Chen Min then ordered his Inspector of Yang province, Gan Zhuo to repel Qian Guang at the Zhuque Bridge (朱雀橋; located on the Qinhuai River near Nanjing).
Gu Rong travelled with Ji Zhan and other scholars from the south, but when they arrived at Xu province, they heard about that the north was becoming increasingly chaotic and hesitated to proceed.
To win the support of the southern gentry clans, Sima Rui appointed him Gu Rong as a Military Judge under him and a Regular Mounted Attendant.