In 697, Zong was serving as deputy minister of defense (夏官侍郎, Xiaguan Shilang) when Wu Zetian gave him the designation of Tong Fengge Luantai Pingzhangshi (同鳳閣鸞臺平章事), making him a chancellor de facto.
Around this time, he developed an enmity with his cousin Wu Yizong (武懿宗) the Prince of Henan (a grandson of Wu Zetian's uncle Wu Shiyi (武士逸)).