Sun Hao, born in 242, is the oldest son of Sun He, a one-time crown prince of the founding emperor Sun Quan, created so following the death of his father Sun Quan's oldest son and first crown prince, Sun Deng, in 241.
Sun Hao’s mother was a concubine of Sun He's, Consort He.
In 250, when Sun Hao was just eight, after Sun Quan tired of constant disputes between Sun He and his brother Sun Ba, the Prince of Lu, he had ordered Prince Ba to commit suicide and deposed Crown Prince He, who was exiled to Guzhang (in modern Huzhou, Zhejiang), presumably with his family, and reduced to commoner status.
Sun Hao thus went from the status of eventual presumed heir to being the son of a commoner, albeit the grandson of the emperor.
Crown Prince He's status had been elevated from commoner status in 252 as Sun Quan, just before his death that year, created him the Prince of Nanyang, with his fief at Changsha.
Indeed, there were rumors, even after Sun He's younger brother Sun Liang took the throne after Sun Quan's death, that the regent Zhuge Ke, an uncle of Sun He's wife Princess Zhang, was interested in restoring Prince He and making him emperor instead.
After Zhuge's assassination and replacement by Sun Jun in 253, however, Prince He fell into danger, as Sun Jun had been instrumental in having him deposed in the first place and wanted to eliminate any chance of a comeback.
Using the rumors as excuse to have Sun He demoted back to commoner status and exiled to Xindu (in modern Hangzhou, Zhejiang), he then sent messengers to force Sun He to commit suicide.
Princess Zhang also committed suicide, but when offered the chance to, Consort He refused—stating that if she died as well, no one would be left to care for Sun He's sons, so she raised Sun Hao and his three brothers by other consorts—Sun De, Sun Qian, and Sun Jun.
Sun Hao was just 11 when his father died.
After Sun Liang was deposed by Sun Jun's cousin and successor Sun Lin in 258, another uncle of Sun Hao's, Sun Xiu, became emperor, and that year, Sun Xiu created Sun Hao and his brothers Sun De and Sun Qian marquesses.
Sun Hao's title was the Marquess of Wucheng, and he was sent to his march (in modern Huzhou, Zhejiang).
At some point, he befriended a magistrate of Wucheng County, Wan Yu, who believed him to be intelligent and studious.
Sun Xiu falls ill in summer 264 and is unable to speak but still can write, so he writes an edict summoning the prime minister Puyang Xing to the palace, where he points and entrusts his son, Sun Wan the Crown Prince, to him.
Sun Xiu dies soon thereafter.
However, Puyang does not follow his wishes but rather, after consulting with the powerful general Zhang Bu, forms the belief that the people are, in light of key ally Shu Han's recent fall in 263, yearning for an older emperor.
(It is not known how old Crown Prince Wan was at this point, but Sun Xiu himself died at age 29, so it was unlikely that Crown Prince Wan was even a teenager.)
At the recommendation of Wan Yu, who is by this point a general, Puyang and Zhang declare Sun Hao emperor instead.
At first, the people of Eastern Wu are impressed with the new emperor, as he reduces taxes, gives relief to the poor, and releases a large number of ladies in waiting from the palace to let them marry.
However, that hopefulness is soon shattered, as Sun Hao starts to be cruel in his punishments, superstitious, and indulging in wine and women.
He also demotes his aunt, Sun Xiu's wife Empress Dowager Zhu to the title of "Empress Jing."
(He honors his mother Consort He as the empress dowager instead, while posthumously honoring his father Sun He with the title Emperor Wen.)
Puyang and Zhang are shocked and disappointed: when their disappointment is reported to the emperor, he has them arrested and executed, together with their clans, late in 264.
In 264, he also creates his wife Marchioness Teng empress.
