Sigma and Aldrich were founded separately in 1935 and 1951, respectively, to supply biochemicals and chemicals to research scientists in the U.S. Both companies started with the production and distribution of a single proprietary chemical: Adenosine triphosphate (ATP) by Sigma and 1-methyl-3- nitro-1-nitrosoguanidine (MNNG) by Aldrich. For many years, the two companies grew independently, Sigma serving primarily biochemists and Aldrich serving organic chemists.

When changing trends in chemical research confirmed the synergy to be realized from their complementary product offerings, Aldrich Chemical Co. merged with Sigma International, Ltd. in 1975, forming Sigma-Aldrich Corporation. With this marriage of broad capabilities and resources, annual double-digit sales growth became the standard in the 1980s and 1990s, with significant expansion in facilities, acquisitions and ventures into new market sectors.

On November 18, 2015, Merck announced the completion of its $17 billion acquisition of Sigma-Aldrich, creating a global leader in the €125 billion industry to help solve the toughest problems in life science. This transaction brought together the world-class products and services, innovative capabilities and exceptional talent of Merck Millipore and Sigma-Aldrich to create a global leader in the life science industry. The company operates as MilliporeSigma in North America.