After he passed the imperial examinations in the Jinshi (進士) class, he was made a copyeditor (校書郎, Xiaoshu Lang) at the Palace Library.
It was said that Song was careful and nonpartisan in his actions, contrary to the partisanship that was rampant among the imperial officials at the time, and that it was thought that his promotions would encourage others to follow his example.
At that time, Wang Shoucheng was particularly powerful due to his command of the imperial Shence Army (神策軍), and his associate Zheng Zhu was openly accepting bribes in exchange for official commissions, drawing much displeasure from Emperor Wenzong.
[3] As part of Emperor Wenzong's and Song's plans to eliminate the eunuchs' power, in 831, Song recommended Wang Fan (王璠) to be the mayor of Jingzhao Municipality (京兆, i.e., the Chang'an region) and secretly informed Wang Fan of Emperor Wenzong's plans.
Song realized that he was being accused of a crime, and, after knocking his writing board on his head, withdrew back to his household to await punishment.
[9] No one dared to openly state that Song was falsely accused, although the mayor of Jingzhao, Cui Guan (崔琯), and the chief judge of the supreme court Wang Zhengya (王正雅) both submitted petitions that the arrested individuals be transferred to the jurisdiction of the proper governmental authorities rather than be held inside the palace — and it was said that it was because of this that the situation did not escalate.
[8] Two days later, Emperor Wenzong summoned the senior officials, including the heads of the various key agencies of the imperial government, to inquire them as to what they opined.
A number of advisory officials, including Cui Xuanliang (崔玄亮), Li Guyan, Wang Zhi (王質), Lu Jun (盧均), Shu Yuanbao (舒元褒), Jiang Xi (蔣係), Pei Xiu (裴休), and Wei Wen (韋溫), begged Emperor Wenzong to reopen the discussions with chancellors and move the entire investigations to the proper governmental authorities.
Meanwhile, Zheng, fearing that the officials would win out and that a second round of investigations would show the truth, suggested to Wang Shoucheng that no executions be carried out, and instead Song should be exiled.
[8] The next day, Li Cou was demoted in title to be the Duke of Chao County, while Song was exiled to be the military advisor to the prefect of Kai Prefecture (開州, in modern Chongqing).
In 836 — after a plot that Emperor Wenzong had with Zheng Zhu (who had, by that point, turned against the eunuchs) and Li Xun to slaughter the eunuchs (known as the Ganlu Incident) failed, leading to Zheng's and Li Xun's deaths — Song's reputation and offices were posthumously restored, and he was given further posthumous honors.