Zhang Yang was known for his bravery, and originally served a mid-level post in his native Bing Province. Under the direction of the governor Ding Yuan, Zhang Yang served under the eunuch Jian Shuo. With the death of Jian Shuo and the rise of the general He Jin, Zhang Yang was sent to fight bandits in Shangdang Commandery.
As a warlord
With He Jin's death and the rise of Dong Zhuo, Zhang Yang attempted to seize Shangdang Commandery for himself, but was unable to do so. When Yuan Shao called for a campaign against Dong Zhuo, Zhang Yang went to join him but was not given significant duties. In 191, the Xiongnu leader Yufuluorevolted and sought Zhang Yang's support; Zhang Yang's refusal resulted in his kidnapping. Yuan Shao's forces eventually defeated Yufuluo and Zhang Yang was freed. After his release, Zhang Yang was appointed by Dong Zhuo as the Administrator of Henei Commandery. In 192, Zhang Yang took in his friend and Dong Zhuo's assassin Lü Bu, who was wanted by Dong Zhuo's successor Li Jue. Lü Bu left for Yuan Shao not long after, only to return in 193. In 194, Lü Bu asked Zhang Yang if he was planning to betray Lü Bu to Li Jue. As Zhang Yang's generals were all bribed by Li Jue, Zhang Yang openly admitted his intention of betraying Lü Bu, while secretly protecting him from Li Jue. Nevertheless, Lü Bu again left Zhang Yang for Zhang Miao not long after. In 195, the general Dong Cheng brought Emperor Xian to Henei Commandery in an attempt to avoid the forces of Li Jue and Guo Si. Zhang Yang's hospitality earned him the appointment of General Who Pacifies the State and the peerage "Marquis of Jinyang". Over the course of the year, Zhang Yang recommended Emperor Xian return to the capital Luoyang, but this was rejected by the emperor's entourage. Finally, in 196, Zhang Yang escorted Emperor Xian back to Luoyang, and also oversaw the reconstruction of the imperial palace. Unlike most other warlords, who kept the emperor for political benefit, Zhang Yang returned to Henei Commandery after the completion of his mission. For his deeds he was promoted to Grand Marshal. In 198, as Cao Cao was preparing to campaign against Lü Bu, Zhang Yang made preparations to assist the latter. These preparations were cut short, however, after he was assassinated by his subordinate Yang Chou, who then attempted to surrender to Cao Cao only to be killed by Sui Gu, who then surrendered to Yuan Shao. The Yingxiong Ji states that Zhang Yang was "of mild and merciful temperament, and under him there were no harsh punishments."
