"Seek truth from facts" is a historically established expression (成語) that first appeared in the Book of Han

Book of Han

The Book of Han, Hanshu or History of the Former Han Dynasty |Fan Ye]] . Various scholars have estimated that the earliest material covered in the book dates back to between 206 and 202 BCE...

. (《汉书·河间献王德传》“河间献王德以孝景前二年立，修学好古，实事求是。从民得善书，必为好写与之，留其真，加金帛赐以招之。”) Originally, it described an attitude toward study and research.

It became a key element of Maoism

Maoism

Maoism, also known as the Mao Zedong Thought , is claimed by Maoists as an anti-Revisionist form of Marxist communist theory, derived from the teachings of the Chinese political leader Mao Zedong . Developed during the 1950s and 1960s, it was widely applied as the political and military guiding...

, first quoted by Mao Zedong

Mao Zedong

Mao Zedong, also transliterated as Mao Tse-tung , and commonly referred to as Chairman Mao , was a Chinese Communist revolutionary, guerrilla warfare strategist, Marxist political philosopher, and leader of the Chinese Revolution...

 during a speech at the Sixth National Congress of the Chinese Communist Party in 1938, in reference to pragmatism

Pragmatism

Pragmatism is a philosophical tradition centered on the linking of practice and theory. It describes a process where theory is extracted from practice, and applied back to practice to form what is called intelligent practice...

. Beginning in 1978, it was further promoted by Deng Xiaoping

Deng Xiaoping

Deng Xiaoping was a Chinese politician, statesman, and diplomat. As leader of the Communist Party of China, Deng was a reformer who led China towards a market economy...

 as a central ideology of Socialism with Chinese characteristics, and applied to economic and political reforms thereafter.