Despite Pei's high status, little is firmly established about his career except for the time that he served as chancellor—as, unusual for a chancellor, he did not have a biography in either the Old Book of Tang or the New Book of Tang. It is known that his clan traced its ancestry to the Cao Wei official Pei Hui (裴徽). Some of Pei Tan's ancestors served as officials for Jin Dynasty (266–420), Former Qin, and Northern Wei, but Pei's several immediate ancestors did not carry any official titles.

As of 710, Pei was serving as minister of justice (刑部尚书) under Emperor Zhongzong, when Emperor Zhongzong died suddenly—a death that traditional historians believed to be a poisoning by Emperor Zhongzong's powerful wife Empress Wei and daughter Li Guo'er the Princess Anle. Empress Wei did not initially announce Emperor Zhongzong's death and quickly made a number of personnel moves in the government and the military. As a part of these moves, Pei was given the designation Tong Zhongshu Menxia Sanpin (同中书门下三品), making him a chancellor de facto. Soon, she had Emperor Zhongzong's son by a concubine, Li Chongmao the Prince of Wen, named emperor (as Emperor Shang), but retained power as empress dowager and regent. Less than a month later, Emperor Zhongzong's sister Princess Taiping and nephew Li Longji the Prince of Linzi, rose in rebellion and killed Empress Dowager Wei and Li Guo'er. LI Longji's father Li Dan the Prince of Xiang became emperor (as Emperor Ruizong), displacing Emperor Shang. Soon, as part of the major governmental reorganization, Pei was demoted to be the prefect of Pu Prefecture (蒲州, roughly modern Yuncheng, Shanxi). That was the last historical record about Pei, and it is not known when he died, although it is known that his son Pei Yuanming (裴元明) later served as a prefectural prefect as well. (There was a reference to Pei Tan in 714, when Pei Tan was listed among a list of secret police officials during the reign of Emperor Zhongzong's mother Wu Zetian in an edict by Li Longji (then reigning as Emperor Xuanzong), indicating that the former secret police officials should be removed from their posts and officially denounced, but it is not completely certain that this was the same Pei Tan.)

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裴谈出自河东裴氏定著五房之一的洗马裴，好佛法。唐中宗时担任御史大夫。以惧内著称，「畏之如严君」，当时有一首描述他的曲子，叫《回波词》：回波尔时栲栳，怕妇也是大好。外边只有裴谈，内里无过李老。706年，在审理神龙革命五王时，大理丞裴谈上奏：「敬晖等人应按皇帝制书处斩、没收财产，不需再行审讯。」因此得到韦后的赞赏，官至刑部尚书。710年六月，中宗死后，唐殇帝即位，韦后任命裴谈为同中书门下三品。韦后被李隆基杀死，唐睿宗登基，八月，裴谈被贬为蒲州刺史。其子裴元明为睦州刺史。

开元初年，唐玄宗诏：「周利贞及滑州刺史裴谈、饶州刺史裴栖贞、大理评事张思敬王承本、华原令康韦、侍御史封询行、判官张胜之刘晖杨允卫遂忠公孙琰、廉州司马锺思廉皆酷吏，宜终身忽齿。」不能确定这个裴谈是不是710年做宰相的裴谈。

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