Born as heir apparent of a vassal prince, Zhu Houcong was not brought up to succeed to the throne. However, the throne became vacant in 1521 with the sudden death of the Hongzhi Emperor's son, the Zhengde Emperor, who did not leave an heir. Prior to Zhengde Emperor's death, the line of succession was as follows:
The 14-year-old Zhu Houcong, then heir presumptive, succeeded to the throne, and so relocated from his father's princedom (near present-day Zhongxiang, Hubei) to the capital, Beijing. As the Jiajing Emperor, Zhu Houcong had his parents posthumously elevated to an "honorary" imperial rank, and had an imperial-style Xianling Mausoleum built for them near Zhongxiang.
Custom dictated that an emperor who was not an immediate descendant of the previous one should be adopted by the previous one, to maintain an unbroken line. Such a posthumous adoption of Zhu Houcong by the Hongzhi Emperor was proposed, but he resisted, preferring instead to have his father declared emperor posthumously. This conflict is known as the "Great Rites Controversy." The Jiajing Emperor prevailed and hundreds of his opponents were banished, flogged in the imperial court (廷杖), or executed. Among the banished was the poet Yang Shen.
The Jiajing Emperor was known to be intelligent and efficient; whilst later he went on strike, and choose not to attend any state meetings, he did not neglect the paperwork and other governmental matters. The Jiajing Emperor was also known to be a cruel and self-aggrandizing emperor and he also chose to reside outside of the Forbidden City in Beijing so he could live in isolation. Ignoring state affairs, the Jiajing Emperor relied on Zhang Cong and Yan Song to handle affairs of state. In time, Yan Song and his son Yan Shifan – who gained power only as a result of his father's political influence – came to dominate the whole government even being called the "First and Second Prime Minister". Ministers such as Hai Rui and Yang Xusheng challenged and even chastised Yan Song and his son but were thoroughly ignored by the emperor. Hai Rui and many ministers were eventually dismissed or executed. The Jiajing Emperor also abandoned the practice of seeing his ministers altogether from 1539 onwards, and for a period of almost 25 years refused to give official audiences, choosing instead to relay his wishes through eunuchs and officials. Only Yan Song, a few handful of eunuchs and Daoist priests ever saw the emperor. This eventually led to corruption at all levels of the Ming government. However, the Jiajing Emperor was intelligent and managed to control the court.
The Ming dynasty had enjoyed a long period of peace, but in 1542 the Mongol leader Altan Khan began to harass China along the northern border. In 1550, he even reached the suburbs of Beijing. Eventually the Ming government appeased him by granting special trading rights. The Ming government also had to deal with wokou pirates attacking the southeastern coastline. Starting in 1550, Beijing was enlarged by the addition of the outer city.
The deadliest earthquake of all times, the Shaanxi earthquake of 1556 that killed over 800,000 people, occurred during the Jiajing Emperor's reign.
The Jiajing Emperor's ruthlessness also led to an internal plot by his concubines and palace maids to assassinate him in October, 1542 by strangling him while he slept. His pursuit of eternal life led him to believe that one of the elixir of extending his life was to force young palace maids to collect morning dew for his consumption. These arduous tasks were performed non-stop even when the palace maids were taken ill and any unwilling participants were executed on the Emperor's whim. A group of palace maids who had had enough of the emperor's cruelty decided to band together to murder him in an event known as the Renyin palace rebellion (壬寅宮變). The lead palace maid tried to strangle the emperor with ribbons from her hair while the others held down the emperor's arms and legs but made a fatal mistake by tying a knot around the emperor's neck which would not tighten. Meanwhile, some of the young palace maids involved began to panic and one (Zhang Jinlian) ran to the empress. The plot was exposed and on the orders of the empress and some officials, all of the palace maids involved, including the emperor's favourite concubine (Consort Duan) and another concubine (Consort Ning, née Wang), were ordered to be executed by slow slicing and their families were killed.
The Jiajing Emperor was a devoted follower of Taoism and attempted to suppress Buddhism. After the assassination attempt in 1542, the emperor moved out of the imperial palace, and lived with a 13-year-old teenage girl who was small and thin, and was able to satisfy his sexual appetite (Lady Shan). The Jiajing Emperor began to pay excessive attention to his Taoist pursuits while ignoring his imperial duties. He built the three Taoist temples Temple of Sun, Temple of Earth and Temple of Moon and extended the Temple of Heaven by adding the Earthly Mount. Over the years, the emperor's devotion to Taoism was to become a heavy financial burden for the Ming government and create dissent across the country.
Particularly during his later years, the Jiajing Emperor was known for spending a great deal of time on alchemy in hopes of finding medicines to prolong his life. He would forcibly recruit young girls in their early teens and engaged in sexual activities in hopes of empowering himself, along with the consumption of potent elixirs. He employed Taoist priests to collect rare minerals from all over the country to create elixirs, including elixirs containing mercury, which inevitably posed health problems at high doses.
After 45 years on the throne (the second longest reign in the Ming dynasty), the Jiajing Emperor died in 1567 – possibly due to mercury overdose from Chinese alchemical elixir poisoning – and was succeeded by his son, the Longqing Emperor. Though his long rule gave the dynasty an era of stability, the Jiajing Emperor's neglect of his official duties resulted in the decline of the dynasty at the end of the 16th century. His style of governance, or the lack thereof, would be emulated by his grandson later in the century.
The Jiajing Emperor was portrayed in contemporary court portrait paintings, as well as in other works of art. For example, in this panoramic painting below, the Jiajing Emperor can be seen in the right half riding a black steed and wearing a plumed helmet. He is distinguished from his entourage of bodyguards as an abnormally tall figure.