He hailed from Pingling 平陵 (near modern Xianyang 咸陽, Shaanxi) and was a appointed erudite (boshi 博士) because of his proficiency in the Confucian Classics. Ping Dang adhered to the school of Confucians that interpreted natural calamities as expressions of Heaven towards the performance of a ruler. He also studied the chapter Yugong 禹貢 "The Tribute of Yu" of the Shangshu 尚書 "Book of Documents" that describes the various provinces of China, their rivers, quality of soil and local products applicable for tribute to the court.
Emperor Cheng 漢成帝 (r. 33-7 BCE) therefore appointed him commandant of cavalry (juduwei 騎都尉) and ordered him to investigate dams and dykes of the empire. When Emperor Ai 漢哀帝 (r. 7-1 BCE) succeeded to the throne, Ping Dang was promoted to Grand Master of Splendid Happiness (guanglu dafu 光祿大夫) and later to Censor-in-chief (yushi dafu 御史大夫) and Counsellor-in-chief (chengxiang 丞相). For that position he was given the title of Marquis within the passes (guanneihou 關內侯).
Just at that time he became seriously ill and planned to decline the imperial order of promotion, yet his relatives forced him to at least accept the title of nobility. Ping Ding, as a man of honour, refused the request of his relatives and declined to accept the official seals, yet the emperor forced him to accept. Ping Dang died shortly after.