The first historical reference to Zhang Xi's own career as an official was in 700, during the reign of Emperor Gaozong's wife Wu Zetian, when Zhang Xi was serving as the deputy minister of civil service affairs (天官侍郎, Tianguan Shilang).
In 701, Zhang Xi was accused of revealing palace secrets and accepting bribes, and he was set to be executed.
When Wu Zetian heard this, she released Su and returned him to office, while setting an execution date for Zhang Xi, but at the last moment spared him and exiled him to Xun Prefecture (循州, roughly modern Huizhou, Guangdong).
In 710, Emperor Zhongzong suddenly died—a death that traditional historians believed to be a poisoning carried out by his powerful wife Empress Wei and daughter Li Guo'er the Princess Anle, so that Empress Wei could become "emperor" like Wu Zetian did and that Li Guo'er could become crown princess.
She conferred on Zhang Xi the designation of Tong Zhongshu Menxia Sanpin (同中書門下三品), again making him chancellor de facto, but had him remain in charge at Luoyang.