His family was originally from Taiyuan, but by the time of his birth was located in Hua Prefecture (華州, roughly modern Weinan, Shaanxi).
Wang Haibin, who was then the commander of Feng'an Base (豐安軍, in modern Wuzhong, Ningxia), served under Xue, who was successful in defeating the Tibetan forces.
Wang Zhongsi later served under the generals Xiao Song and Li Hui (李褘) the Prince of Xin'an (Emperor Xuanzong's second cousin).
By 733, Wang was a general, serving at Hexi Circuit (河西, headquartered in modern Wuwei, Gansu) and carrying the title of Baron of Qingyuan.
Wang subsequently contributed much to a victory over Tubo, and was promoted back to general status, and was soon made the deputy military governor (jiedushi) of Hedong Circuit (河東, headquartered in modern Taiyuan).
In 746, Wang was given the military governorships of Hexi and Longyou (隴右, headquartered in modern Haidong Prefecture, Qinghai), but continued to oversee Hedong and Shuofang as well.
It was also said that, however, he was far more familiar with the people of Hedong and Shuofang than with Hexi and Longyou, and was not as good in governance of those circuits, and that he had gotten arrogant and wasteful in light of his successes, causing his reputation to suffer.
Wang, instead, led the troops himself to Xiongwu in advance of the rendezvous date and, after participating in the building project, returned with the soldiers, and submitted reports to Emperor Xuanzong that he believed An was planning treason.
Meanwhile, Emperor Xuanzong considered ordering Wang to attack Tubo's Shibao Castle (石堡城, in modern Xining, Qinghai).
Wang's subordinate Geshu Han, whose achievements impressed Emperor Xuanzong, was made the military governor of Longyou, in his absence.
When Geshu was subsequently summoned to Chang'an to meet with Emperor Xuanzong, his subordinates suggested that he bring much treasure to bribe the central government officials to try to save Wang.
Emperor Xuanzong initially became irritated and refused to talk with him further, but Geshu kneeled, hit the ground with his head, and cried bitterly.
Emperor Xuanzong relented and spared Wang, but demoted him to be the governor of Hanyang Commandery (漢陽, in modern Wuhan, Hubei).