Deloitte Touche Tohmatsu Limited
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Company History
Founded 1845 in London, United Kingdom
William Welch Deloitte opened an accounting office in London in 1845. The modern Deloitte network took shape through the histories and mergers of Deloitte, Haskins & Sells, Touche Ross, and Tohmatsu.
Deloitte possesses a deep, historic founding legacy, tracing its roots to the dawn of modern corporate accounting during the industrial expansion of 19th-century London and New York. The modern conglomerate is the product of a series of historical mergers, but the foundational name traces back to William Welch Deloitte. In 1845, at the height of the British Railway Mania, Deloitte opened a small accounting office in London. He was a brilliant, meticulous accountant. He achieved historical significance in 1849 when he was appointed as an independent auditor for the Great Western Railway. He was the very first independent accountant ever appointed to audit a public company, establishing the foundational principle of independent corporate oversight. The second foundational pillar was established across the Atlantic in 1890, when Charles Waldo Haskins and Elijah Watt Sells founded Haskins & Sells in New York. They were brilliant American accountants who gained national fame when they were hired by the US Congress to overhaul the chaotic accounting system of the United States Government. In 1893, they also established the precedent of professional American accounting. The third pillar was the firm Touche Ross, founded in 1899 by George Touche in London (and later expanding into the US). In 1989, recognizing the requirement for global scale to serve multinational clients, Deloitte Haskins & Sells executed a historic merger with Touche Ross. This consolidation formed Deloitte & Touche (now simply known as Deloitte), creating a globe-spanning professional services titan built upon the foundational legacy of the very men who invented modern corporate auditing.
William Welch Deloitte opens an accounting office in London, establishing the Deloitte lineage.
George Touche establishes a predecessor firm that later becomes part of the Deloitte & Touche lineage.
Nobuzo Tohmatsu helps establish the Japanese firm that becomes part of Deloitte's global network identity.
Deloitte Haskins & Sells and Touche Ross combine to form Deloitte & Touche in a major professional-services merger.
The global network increasingly uses the Deloitte brand across member firms and service lines.
Joe Ucuzoglu becomes Deloitte Global Chief Executive Officer.
Deloitte reports $70.5B in aggregate global revenue for FY2025.
Deloitte acquired Monitor Group, a strategy consulting firm founded by Michael Porter, out of bankruptcy to add top-tier strategy consulting capabilities to its advisory practice. Monitor had gone bankrupt in 2012 following the loss of major client revenue during the financial crisis, but its brand and talent were valuable assets.
Deloitte acquired ConvergEx, a technology solutions provider for the financial services industry, to strengthen its financial services technology advisory and implementation capabilities at a time when capital markets firms were investing heavily in trading infrastructure and compliance systems.
Touche Ross merged with Deloitte Haskins & Sells in 1989 to form Deloitte & Touche, combining two of the Big Eight accounting firms as the profession was consolidating. The merger was driven by competitive pressure from the larger Arthur Andersen and Price Waterhouse firms and created a combined entity with greater global reach and client scale.
Since its establishment in 1845, Deloitte Touche Tohmatsu Limited expanded from an early-stage venture into a recognized leader in Professional services, accounting, tax, consulting, and advisory, overcoming key market challenges.
Over its history, Deloitte Touche Tohmatsu Limited executed decisive strategic pivots toward scalable monetization and digital distribution, securing its current market leadership.
By continually modernizing operations and embracing workflow automation, Deloitte Touche Tohmatsu Limited maintains resilience through changing technological and economic cycles.