Corporate address: 1166 Avenue of the Americas, New York, NY 10036, USA
Founded: 1871
Employees: 85,000+
Annual revenue: $27.0 billion (2025)
Annual revenue (risk & insurance services): $17.3 billion (2025)
Key people: John Q. Doyle (president & CEO), Pat Tomlinson (president & CEO, Mercer), Dean Klisura (president & CEO, Guy Carpenter), Martin South (president & CEO, Marsh), Nick Studer (president & CEO, Oliver Wyman Group)
Marsh McLennan Companies (MMC) is a professional services firm that’s behind some of today’s major insurance and consulting players, including Marsh, Guy Carpenter, Mercer, and Oliver Wyman. The company was founded by Henry W. Marsh and Donald R. McLennan, who merged their two firms in 1904 to create the largest insurance agency in the world. Before the merger, Marsh had seen an opportunity for insurance brokers to distribute risks across firms following the Great Fire of 1871, which wiped out many insurers.
Today, Marsh is an insurance broking and risk management giant, with offices around the world. Meanwhile, Guy Carpenter offers reinsurance broking expertise as well as strategic advisory services and analytics. Oliver Wyman is a global management consulting firm and Mercer is a human resources consulting firm.
In April 2019, MMC completed a US$5.6 billion acquisition of Jardine Lloyd Thompson Group plc (JLT). Already the largest insurance broker in the world, Marsh advises around 95% of Fortune 1000 companies. Following the acquisition, the firm announced that the deal significantly expanded its presence in the middle market and small commercial sectors, while also bringing an influx of around 10,000 talented individuals.
Marsh McLennan in the news
March 2021: Marsh & McLennan Companies announces rebrand
October 2021: Marsh McLennan launches Cyber Risk Analytics Center
November 2021: Marsh McLennan makes swathe of key leadership changes
November 2021: Marsh McLennan secures new partnership to bolster clients' cybersecurity
December 2021: Marsh McLennan names new climate executive
March 2022: Marsh McLennan exits Russia
March 2022: Marsh McLennan names new SVP, general counsel
April 2022: Marsh McLennan shares net zero commitment
September 2022: Marsh McLennan names John Doyle new president and CEO
November 2022: Marsh McLennan joins up with UN-backed resilience initiative
February 2023: Marsh McLennan names CEO for US and Canada
February 2023: Marsh McLennan appoints UK chief executive
April 2023: Marsh McLennan expects to see costs of up to US$400 million from restructuring program
May 2023: Marsh McLennan stockholders elects board of directors
June 2023: Marsh McLennan to help facilitate insurance access for Ukraine
Key people
John Q. Doyle – President & CEO, MMC
Doyle took over the role of president and chief executive officer of Marsh McLennan in January 2023. Prior to this, he served as group president and chief operating officer. He joined MMC in 2016 as president of Marsh and led the firm as president and CEO from 2017 to 2021.
Doyle boasts more than three decades of management experience, which began in AIG. At the insurance giant, he held several leadership roles, including as CEO of AIG Commercial Insurance, president and CEO of AIG US Property and Casualty, president of National Union Fire Insurance Company, and president of American Home Assurance Company.
Dean Klisura - president & CEO, Guy Carpenter
Klisura commenced his role as president and CEO of Guy Carpenter in October 2020. He also serves as vice-chair of MMC. Before joining Guy Carpenter, Klisura held the role of president of Marsh Global Placement and Advisory Services. He joined March in 1993 and served several global leadership positions, including president of Global Specialties.
Martin South – president & CEO, Marsh
South became president and CEO of Marsh in January 2022. He also serves as vice-chair of MMC. He first joined Marsh in 1985 with Bowring Marsh, an MMC broking unit. South boasts more than three decades in the insurance industry. This includes leadership stints with Zurich Financial Services, where he was a member of the group management board and CEO of Zurich’s London operations. South rejoined Marsh in 2007 and has since served as CEO of Asia-Pacific region, CEO of UK and Ireland, CEO of Europe, and CEO of US and Canada.
Nick Studer – president & CEO, Oliver Wyman Group
Studer was names president and CEO of Oliver Wyman Group in July 2021. He also serves as vice-chair of MMC. Prior to his appointment, Studer was managing partner of Oliver Wyman. He has also held several leadership positions within the firm, including as managing partner of the Consumer, Industrial, and Services Practice, managing partner of the Financial Services Practice, and head of the European Finance and Risk Practice. Studer has more than two decades of experience in consulting in the UK, Continental Europe, and North America.
