[1]: 316ff, 398f [2][3] As the head of Ranbaxy, Singh oversaw both a massively fraudulent operation aimed at deceiving the U.S. Food and Drug Administration (FDA) and other international health organisations as to the quality of the company's generic drug products, as well as the deception of the company's buyers when he mediated its sale to the Japanese drugmaker Daiichi Sankyo, in 2008.

[4][1]: 316ff, 398f  Singh, who had been kept on as CEO by the purchasing company, resigned in 2009, as the deceit became apparent and as Ranbaxy began posting losses due to FDA-imposed restrictions on its products.

[1]: xvii, 115  His tenure as head of the firm coincided with a period of intense, whistleblower-driven fraud investigations by the FDA, other world health organisations, as well as the U.S. Department of Justice (DOJ).

[4][1] In 2008, Singh orchestrated the fraudulent sale of Ranbaxy to the Japanese pharmaceutical Daiichi Sankyo for U.S.$2-billion, which included the 33.5% stake owned by him and his brother.

[4][1] This was followed by further events implicating Singh in illegal activity while at the Ranbaxy helm, including a fraud prosecution of the company by the DOJ that resulted in a corporate guilty plea and a U.S.$500,000,000 fine in May 2013;[1]: 316ff [1] Daiichi Sankyo launched a legal case against the Singhs at the International Court of Arbitration in Singapore, which directed the brothers in April 2016 to pay U.S.$550,000,000 to the Japanese company.