Zhang Yanhan was born in 884. He was from Suiyang, but little is stated about his family background in the traditional sources. Late during Tang, he served as the military advisor to the prefect of Shan Prefecture. However, at one point, he took a leave to see his uncle Zhang Shensi, who was then serving as the acting military governor of Ganhua Circuit. He informed Zhang Shensi his opinion that northern China was about to fall into complete chaos and that he wanted to head to the region between the Yangtze and Huai Rivers, so that the family line could be extended. Zhang Shensi agreed with his analysis and sent him on his way.
During Wu
Tang ended in 907, and the realm fractured into several states, with Yang Xingmi's domain, then ruled by his son and successor Yang Wo, becoming the state of Hongnong. Zhang Yanhan initially served there as the magistrate of Yancheng County, and was said to have been capable. He was later promoted to be the military commander of the army at Chu Prefecture. In 918, when then-Wu regent Xu Wen's adoptive son Xu Zhigao became junior regent at Wu's capital Guangling , Xu Zhigao was given the title of military prefect of Jiang Prefecture, but obviously could not govern Jiang himself from Guangling; therefore, he sent Zhang there, as his secretary, to actually govern the prefecture. At a later point, Zhang returned to the Wu imperial government to serve as an imperial censor, and was put in charge, in an acting capacity, of the office of the imperial censors. At that time, the general Zhang Xuan was one of the commanders of the guards for the capital Guangling, and was, due to his accomplishments, arrogant and violent. Zhang Yanhan submitted an indictment against Zhang Xuan, which caused other similarly arrogant generals to become apprehensive and to curb their behavior. Zhang Yanhan was later promoted to be the deputy minister of rites. This caused him to appreciate Xu Zhigao greatly, as he had not previously been considered a close associate of the regent. At that time, Wu had not held imperial examinations — a Tang tradition for selecting officials for the imperial government; rather, it would be that people would be selected based on contents of petitions they submitted. Xu put Zhang in charge reinstituting the imperial examinations, and Zhang performed the task capably, paying attention to promoting the impoverished and not being intimidated by those with honored backgrounds, such that the administrators under him were respecting him as if he were a deity. After Xu Zhigao's son Xu Jingtong became junior regent in 930, Xu Jingtong was impressed with Zhang, and stated to others, "Mr. Zhang's opinions are fair and his decisions are well-reasoned. His listing of matters are detailed and clear. I should listen to him wholeheartedly." Zhang eventually was put in charge of overseeing all six ministries of the executive bureau of government and became respected by the people. When he was in his 50s, he was given the titles of Zhongshu Shilang and Tong Zhongshu Menxia Pingzhangshi, making him a chancellor. Even though he was by no means old, the people still commented at the time that it was regrettable that he was not chancellor earlier.
During Southern Tang
In 937, Xu Zhigao had Yang Pu yield the throne to him, ending Wu and starting a new state of Southern Tang, with Xu as its emperor. He commissioned Zhang Yanhan, as well as fellow former Wu chancellors Zhang Juyong and Li Jianxun, chancellors of his new state. It was said that some time thereafter, Zhang Yanhan fell ill. As Li Bian still hoped that Zhang would be able to serve as chancellor, he did not allow Zhang to resign, but rather repeatedly send emissaries to oversee his treatment and make sure that he was given the best medications. Despite this, Zhang died around the new year 941. He was given posthumous honors.
