Along with six of his classmates including Huang Yong (黄镛) and Lin Zezu (林则祖) Chen sent a letter to politician Ding Daquan (丁大全) accusing him of mishandling defences against Mongol invaders from the north.
In the spring of 1275 CE, Jia Sidao was sacked from his position and Chen appointed Prime Minister by Grand Empress Dowager Xie (謝太皇太后), who held power on behalf of the underage Emperor Gong of Song.
The letter claimed that the Prime Minister was a hesitant and vacillating army commander who could not direct his soldiers properly - "Zhang Shijie's brave infantry are at sea whilst the navy is on the march".
In December of the same year, Chen despatched minister Liu Yue (柳岳) to approach the camp of the advancing Mongol army and sue for peace but its commander Bayan of the Baarin refused to negotiate.
In the first lunar month of the second year of the Deyou era (1277 by the Julian Calendar), the Mongol Army arrived at Nieiting Mountain (臬亭山), in the northern suburbs of modern-day Hangzhou, Zhejiang Province.