Qian Hongzong was probably born in 928. His father was Qian Chuanguan (later known as Qian Yuanguan, King Wenmu), who, as of 928, had been designated the heir to his father (Qian Hongzong's grandfather) Qian Liu (King Wusu), the founding king of Wuyue. His mother was Qian Chuanguan's concubine Lady Fu, who had previously given birth to Qian Chuanguan's oldest biological son (fifth son overall) Qian Hongzun. Qian Hongzong was Qian Chuanguan's seventh son (third biological). When Qian Hongzong was born, Qian Chuanguan dreamed of a man presenting him with a box of gold, and therefore nicknamed Qian Hongzong Wanjin ("10,000 catties of gold").
Early in his career, Qian Hongzong served as an officer of the Wuyue royal guard corps, and carried the honorary title of acting Sikong (司空, one of the Three Excellencies). In 944, during the reign of his older brother Qian Hongzuo (King Zhongxian), who had succeeded Qian Yuanguan, he was sent to Yue Prefecture (越州, in modern Shaoxing, Zhejiang) to serve as the comforter of the eastern headquarters (i.e., Yue), and was given the honorary title of acting Taiwei (太尉, also one of the Three Excellencies). In 947, Qian Hongzuo recalled him to Wuyue's capital Qiantang to serve as chancellor. Later in the year, Qian Hongzuo died, and, in his will, named Qian Hongzong the military governor (Jiedushi) of Wuyue's two main circuits, Zhenhai (鎮海, headquartered at Qiantang) and Zhendong (鎮東, headquartered at Yue), as well as the honorary chancellor title of Shizhong (侍中). Shortly after, Qian Hongzong took the throne. For the time being, he used the Huitong era name of the Khitan Liao dynasty, as Qian Hongzuo had previously submitted to Liao as a vassal.
After Qian Hongzong took the throne, he recalled his younger brother Qian Hongchu, who was then serving as the prefect of Tai Prefecture (台州, in modern Taizhou, Zhejiang), to Qiantang, to serve as acting chancellor. Shortly after, the warlord Li Da, who controlled Weiwu Circuit (威武, headquartered in modern Fuzhou, Fujian), arrived from Weiwu to pay homage to him. Qian Hongzong granted Li Da an honorary chancellor title, and gave him a new name, Li Ruyun. Li, fearing that Qian Hongzong would detain him at Qiantang, bribed the powerful royal guard general Hu Jinsi, and Hu spoke on his behalf, asking Qian Hongzong to return Li to Weiwu. Qian Hongzong agreed. Shortly after, Li, who was beginning to have conflicts with the Wuyue general Bao Xiurang (鮑修讓), whose army was stationed at Fu to both help him defend the city and watch his moves, and was plotting to assassinate Bao and surrender the city to Wuyue's neighbor Southern Tang. When Bao realized this, he ambushed Li and slaughtered Li's family.
In winter 947, Later Han's emperor Liu Zhiyuan, who had taken over the Central Plains after Liao withdrawal, bestowed on Qian Hongzong the titles of Generalissimo of the Southeast Armies (東南兵馬都元帥, Dongnan Bingma Du Yuanshuai), military governor of Zhendong and Zhenhai, Zhongshu Ling (中書令), and Prince of Wuyue. It was only at this point that Qian Hongzong accepted Liu as his lord and started to use Later Han's era name. At a later point, Later Han bestowed the greater title of king (Guowang (國王), compared to simply Wang (王, "prince")) on Qian Hongzong, although it was not clear when. As king, Qian Hongzong was said to be strict, as he believed that Qian Hongzuo was overly lenient such that the generals had too much power, effectively depriving the king of ability to make decisions. After he became king, he executed three administrators of Zhenhai and Zhendong that he considered to be abusing power.
Hu continued to have substantial power in the governance of the state, drawing Qian Hongzong's displeasure, and the king considered sending him out to be a prefect of a prefecture, but Hu declined. Nevertheless, from this point on, Hu's suggestions were often met with rebuke, such that Hu built a small shrine to Qian Hongzuo in his home, offering sacrifices there and shedding bitter tears. There was one occasion when Qian Hongzong was reviewing the troops and announced an award for them. Hu thought that the award was excessive and argued against it, but the young king angrily threw his pen in to the water and stated, "My wealth is to be shared with the soldiers. How is it that there can be a limit to that?" There was also once an incident where a civilian was accused of slaughtering a cow privately (i.e., without paying the taxes for doing so). The investigating officer claimed that the civilian had 1,000 illegitimate catties of meat from the incident. Qian Hongzong turned to Hu and asked, "What much does the largest cow weigh?" Hu responded, "No more than 300 catties." Qian Hongzong then responded, "Then, the only conclusion is that the investigating officer's accusations were false." He ordered the investigating officer punished. When Hu congratulated him on his intelligent ruling, he responded, "How did you know about this, Lord?" Hu, stuttering, responded, "Before your subject joined the army, I used to do this." However, Hu believed that Qian already knew of his past and was merely intending to embarrass him publicly (as being a butcher was not considered an honorable profession), and therefore was even more unhappy about the king, particularly because the king also repeatedly rebuked him over the situation with Li Ruyun.
Around new year 948, Qian Hongzong began to discuss with two officials that he felt he could trust, He Chengxun (何承訓) and Shuiqiu Zhaoquan (水丘昭券), on possibly expelling Hu from the headquarters. Shuiqiu thought it might be dangerous to do so due to Hu's hold on the army, and therefore Qian hesitated. He Chengxun, fearful that the news might leak, instead decided to leak it to Hu himself. One night, when Qian was holding a feast, Hu thought that Qian was intending to act against him then, and therefore gathered his soldiers and headed for the king's mansion. He surrounded the mansion and put the king under house arrest, and the issued an order in the king's name, claiming that the king had suffered a stroke and was therefore passing the throne to his younger brother Qian Hongchu. When he went to offer the throne to Qian Hongchu, Qian Hongchu agreed, on the condition that Qian Hongzong's life be spared. When Hu agreed, Qian Hongchu took the throne (as King Zhongyi). As part of the coup, Hu killed Shuiqiu and Qian Hongzong's uncle (Lady Fu's brother) Fu Guangxuan (鄜光鉉).
Qian Hongchu moved Qian Hongzong to their grandfather Qian Liu's old mansion at Yijin Base (衣錦軍, in modern Hangzhou), effectively under house arrest, and sent his trusted officer Xue Wen (薛溫) to guard the mansion. He secretly instructed Xue, "If there were to be unusual orders , it would not be out of my will. You should resist to the death."