Guo Tu was from Yingchuan Commandery (潁川郡), which is around present-day Xuchang, Henan.
He started his career as a subordinate of Han Fu, the Governor of Ji Province.
In 191, Guo Tu, along with Xin Ping, Xun Chen and others, managed to convince Han Fu to relinquish his governorship to the warlord Yuan Shao.
In 195, the Han Emperor Xian called for help from the lords, pleading them to escort him and the imperial court away from the tyrants Li Jue and Guo Si.
As a result, the much less powerful warlord Cao Cao took Emperor Xian into his capital of Xuchang and issued many edicts in the Emperor's name, including a harshly worded edict condemning Yuan Shao for conquering Han provinces from other governors.
During the Battle of Boma in 200, Yuan Shao ordered Yan Liang, with Guo Tu and Chunyu Qiong providing support, to lead troops to attack Boma (白馬; near present-day Hua County, Henan), which was defended by Liu Yan (劉延), a military officer under Yuan Shao's rival Cao Cao.