He had his most powerful positions during the reign of Later Tang's last emperor Li Congke, as both chancellor and the director of the three financial agencies (taxation, treasury, and salt and iron monopolies).
[4] At some point, Zhang fostered his relationship with Li Siyuan's chief strategist An Chonghui by giving a daughter in marriage to An's son.
[7] The directorate of material pricing — which Later Liang had established to replace Tang's three financial agencies (taxation, treasury, and salt and iron monopolies) and merge them into one — was abolished.
[7] He was also apparently, at the same time, serving as the military governor of Zhongwu Circuit (忠武, headquartered in modern Xuchang, Henan).
[9] In 930, Zhang Yanlang was given the titles of acting minister of public works (工部尚書, Gongbu Shangshu) and director of the three agencies (三司使, Sansishi).
[11] In early 936, Li Congke, concerned that his brother-in-law (the husband of Li Siyuan's biological daughter the Princess of Jin), Shi Jingtang the military governor of Hedong Circuit (河東, headquartered in modern Taiyuan, Shanxi), would rebel, consulted a number of imperial officials on what to do to ward off a Hedong rebellion.
Zhang was very supportive of Lü's proposal, believing that not only would it ward off a Hedong rebellion, but it would create great savings in border defenses.
The result of the conscription order only yielded 5,000 soldiers and 2,000 horses, creating no real help for the imperial army but causing the people much alarm.
Li Congke, believing the situation to be hopeless, committed suicide with his family by fire, ending Later Tang.
At the gathering, he declared a general pardon for all present — except for Zhang Yanlang, whom he arrested and put into jail.