Founded in 1879 by Algernon Sydney Sullivan and William Nelson Cromwell, the firm advised on the creation of Edison General Electric and the formation of U.S. Steel, pioneered modern reorganization efforts for insolvent companies, and influenced key financial and regulatory practices.

Sullivan & Cromwell handled landmark deals, including Ford Motor Company's $643 million offering in 1956, and adapted to evolving business trends by establishing dedicated banking and mergers and acquisitions units.

It was among the first U.S. firms to open overseas offices, although its history includes controversial actions such as aiding Nazi Germany's arms buildup and involvement in the 1954 Guatemalan coup d'état.

Sullivan & Cromwell's lawyers have been involved in various controversies, including insider trading scandals, work with tobacco companies, and criticism for its role in the FTX cryptocurrency exchange collapse.

[8] The firm also worked with less-successful businesses during the volatile decades before the establishment of modern federal bankruptcy laws; it pioneered efforts to reorganize insolvent companies through what became known as the "Cromwell plan.

[10] During the Great Depression and its aftermath, the firm litigated in the newly emerging fields of shareholder derivatives, antitrust actions, federal income tax law, and registration under the Securities Act of 1933.

Evolving business trends continued to be reflected in the firm's organization; a banking practice was formed in 1968, and a mergers and acquisitions unit was established in 1980, as M&A began to accelerate.

In 1935, Allen Dulles, then a partner in the firm and later Director of Central Intelligence, visited Germany and returned somewhat disturbed by the direction of the regime.

[26][27] In 2008, police uncovered an insider trading conspiracy involving a former Sullivan & Cromwell attorney; Toronto Dorsey & Whitney partner Gil Cornblum had discovered inside information at both Sullivan & Cromwell and Dorsey and, with his co-conspirator, a former lawyer and Cornblum's law school classmate, was found to have gained over $10 million in illegal profits over a 14-year span.

[28] Cornblum committed suicide by jumping from a bridge as he was under investigation and shortly before he was to be arrested but before criminal charges were laid against him, one day before his alleged co-conspirator pleaded guilty.

Senators published a letter arguing that Sullivan and Cromwell had a conflict of interest as FTX bankruptcy counsel due to its significant pre-bankruptcy work.

[33][34] Law Professors Jonathan Lipson and David Skeel argue that as FTX was nearing bankruptcy, Sullivan and Cromwell urged then-CEO Sam Bankman-Fried to transfer control of the company to John J. Ray III by making false promises about Ray's role and failed to suggest that Bankman-Fried and others might face criminal liability.