Li Jingxuan's activities during the earliest years of Emperor Gaozong's reign are not clear, but as of the early part of Emperor Gaozong's Qianfeng era (666-668), he was serving as a mid-level official at the legislative bureau of government (西臺, Xi Tai), as well as an imperial scholar.
He also received the designation of Tong Dong Xi Tai Sanpin (同東西臺三品), making him a chancellor de facto.
Li adopted the regulations and forms that Zhang drafted, and was able to make the civil service system more efficient than before, and it was said that since the start of Emperor Gaozong's reign, many officials had been in charge of civil service, but few were good at their duties, with Li being an exception and praised for his abilities.
The reserve officials who visit Chang'an to request positions number in the thousands each year, and it was said that Li was capable of remembering their names and their strengths and weaknesses.
Xu had, while serving as a prefectural official, encountered the situation where his colleague Zhang Hui (張惠) was due to be executed for receiving bribes.
Emperor Gaozong was incensed, and demoted him to the post of prefect of Heng Prefecture (near modern Hengyang in Hunan).
After some time, he was promoted slightly to be the secretary general to the commandant at Yang Prefecture (揚州, roughly modern Yangzhou, Jiangsu).
His brother Li Yuansu later served as a chancellor during the reign of Emperor Gaozong's wife Wu Zetian.