He was the youngest son of the dynasty's founder Emperor Wu, and he governed the modern Sichuan and Chongqing region.
While serving in that capacity, Xiao Ji carried out a greater development of the economy and also expanded Liang territory deeper into non-Han areas.
After Jiankang fell and Emperor Wu died in 549, Xiao Ji finally took action in spring 550, sending a 30,000-men force commanded by his heir apparent Xiao Yuanzhao (蕭圓照), and he claimed that he was willing to have that force accept orders from his brother Xiao Yi the Prince of Xiangdong—the governor of Jing Province (荊州, modern central and western Hubei) and at that time the strongest Liang prince, who was exercising imperial authority at the time.
In winter 550, Xiao Ji departed Chengdu with his forces and headed east on the Yangtze River.
He also attached a note, "Based on geography, you and I are like Liu Bei and Sun Quan, and we should each be satisfied with our territory.
Xiao Ji's son Xiao Yuanzheng (蕭圓正) the Marquess of Jiang'an was the governor of Xiyang Commandery (roughly modern Huanggang, Hubei), and he enjoyed great support from the people, and his army had grown to 10,000-men strong.
Also in summer 551, Hou Jing launched a major attack on Xiao Yi, and Xiao Yi, hoping for support from Western Wei, ordered his cousin Xiao Xun (蕭循) the Marquess of Yifeng, the governor of Liang Province (梁州, modern southern Shaanxi), to abandon the provincial capital Nanzheng (南鄭, in modern Hanzhong, Shaanxi) and cede Nanzheng to Western Wei.
At that time, flowers were growing from the columns of his mansion, and he believed it to be a divine sign of favor, and he therefore declared himself emperor.
When his subordinates Wang Senglüe (王僧略, Wang Sengbian's brother) and Xu Peng (徐怦) advised against the action, he had them killed—an action that caused his cousin Xiao Hui (蕭撝), whom he had created the Prince of Qin Commandery, to sigh and comment that killing skillful men was a sign of impending disaster.
Xiao Ji therefore led his forces and departed from Chengdu, planning to confront Hou.
Xiao Ji sent Qiao Yan to head back to Chengdu to try to lift the siege, and by now, he became aware that Hou had been destroyed.
Despite the difficult situation that he was in, however, Xiao Ji was refusing to distribute his considerable wealth to his soldiers to try to encourage them to fight; as a result, the morale sank.
Another of Xiao Yi's generals, Fan Meng (樊猛), crushed his remaining force and surrounded his ship to prevent him from fleeing.
Xiao Yi sent a secret order to Fan, "If that person remains alive, then this is no success."