On 22 January 239, Cao Rui died leaving the adopted child
Cao Fang to ascend the throne. A regency ensued with Sima Yi and imperial kinsman
Cao Shuang in charge but the pair fell apart and Cao Shuang would push Sima Yi into retirement. Wang Guan however is said to have opposed Cao Shuang's attempts to abuse his power. When Cao Shuang sought timber for personal use, Wang Guan raided the timber office, and he repeatedly enforced laws to prevent Cao Shuang getting access to treasuries within the government offices. As Cao Shuang felt uncomfortable with Wang Guan for this reason, he demoted Wang Guan to Minister Coachman (). However, the records are known to be hostile towards Cao Shuang and there may have been other reasons Cao Shuang moved a Sima Yi partisan to another ministerial role.
Sima Yi launched a
coup against his rival on 5 February 249. Wang Guan participated in the coup by becoming a temporary general, the Central Commander of the Army (), the position of Shuang's brother Cao Xi () and taking over Cao Xi's troops. After Cao Shuang was executed on 9 February, Sima Yi arranged for Wang Guan to receive the title of a Secondary Marquis () and was appointed as a Master of Writing () and Chief Commandant of Escorting Cavalry (). In 254,
Cao Fang had grown up and sought to overthrow his controller, Sima Yi's son
Sima Shi but the plots failed and Cao Fang was deposed and jailed for life on 17 October. Sima Shi and his ministers, following the precedent of the deposed
Former Han Liu He, accused Cao Fang of being a sexual deviant morally unworthy of the throne with Wang Guan one of the names to sign these accusations. When the young
Cao Mao came to the throne, Wang Guan was promoted to Marquis of Zhongxiang Village () and made a Household Counsellor () and Left Supervisor of the Masters of Writing (). On 2 June 260,
Cao Mao sought to free himself from his controller
Sima Zhao, Sima Shi's brother, but was killed in the streets by Sima loyalists. On 27 June, the last Wei Emperor,
Cao Huan ascended the throne. Wang was also appointed as
Excellency of Works(), reaching one of the three highest ministerial posts. However, unlike during Cao Fang's abdication, Wang Guan's name is not listed on any of the memorials around Cao Mao's death and Wang Guan tried to refuse the promotion. Sima Zhao rejected the refusal and dispatched an envoy. Wang Guan took the post but resigned, hanging up his seals of office and returned home. == Death and legacy ==