At some point, he became a chief secretary at the county government of Mianchi (澠池, in modern Sanmenxia, Henan), but abandoned his post to serve Zhu Quanzhong, then a powerful warlord and military governor of Xuanwu Circuit (宣武, headquartered in modern Kaifeng)[4] — notwithstanding the fact that his father had previously served Zhu but had been exiled after being accused of faults.
In 909, when he was serving as one of Zhu's attendants, he was made a general of the imperial guards and one of the monitors of the army against Later Liang's archenemy to the north, Jin.
[4] In late 911, as Emperor Taizu was returning from a campaign against Jin, he made a stop at Huojia (獲嘉, in modern Xinxiang, Henan), within Huai Prefecture.
Emperor Taizu's chief advisor Li Zhen, however, did not consider Duan an appropriate person for that role and sought to have him removed.
With the main Jin army in the north, the defense of the key border city Wei Prefecture (衛州, in modern Xinxiang, Henan) was left in the hands of its prefect Li Cunru (李存儒), an adoptive brother of Jin's prince Li Cunxu.
In fall 922, Duan, along with another officer, Zhang Lang (張朗), launched a surprise attack on Wei Prefecture, capturing it and taking Li Cunru captive.
Duan subsequently rendezvoused with the supreme commander of the Later Liang forces against Jin, Dai Siyuan, and captured a number of other nearby Jin garrisons — Qimen (淇門, in modern Hebi, Henan), Gongcheng (共城), and Xinxiang (新鄉, both in modern Xinxiang).
[7] In 923, shortly after Li Cunxu declared himself emperor of a new Later Tang (as its Emperor Zhuangzong), he sent his adoptive brother Li Siyuan to launch a surprise attack on a major Later Liang city south of the Yellow River, Yun Prefecture (鄆州, in modern Tai'an, Shandong) and captured it.
This left the Later Liang capital Daliang (i.e., Kaifeng) relatively defenseless, and Zhu Zhen, in fear and anger, removed Dai (as he believed Dai to be responsible for leaving Yun Prefecture open to attack) and replaced him with Wang Yanzhang, with Duan serving as Wang's deputy.
[8] A quick counterattack by Wang captured the southern half of Desheng (德勝, in modern Puyang, Henan) (i.e., the southern part of the city south of the Yellow River), and Wang subsequently put Yangliu (楊劉, in modern Liaocheng, Shandong) under siege, to try to cut off the communications between Later Tang proper and Yun Prefecture.
However, Zhu Zhen's close associates Zhao Yan (Zhu Zhen's brother-in-law) and four brothers/cousins of his deceased wife Consort Zhang were fearful that Wang was resentful of their influence on the governance — as Wang often spoke of wanting to kill the evildoers after he achieves victories on the battlefield, which they believed to be targeting them.
Under the advice of Kang and Guo Chongtao, Emperor Zhuangzong, instead of taking up Duan's challenge, took his main forces and swiftly went to Yun Prefecture to rendezvous with Li Siyuan, and then confronted the smaller army that Wang and Zhang commanded.
With Duan's army trapped north of the Yellow River and unable to return to Daliang to defend it, Zhu Zhen, believing capture to be imminent, committed suicide, ending Later Liang.
[4][5][8] Li Shaoqin was subsequently made full military governor of Yicheng, and then moved to Taining Circuit (泰寧, headquartered in modern Jining, Shandong).