In 1828, Henry Willis began selling imported goods for commission on the Baltic Exchange in London.

[3] In the 1950s, the company's actuary business grew significantly as private pensions gained usage.

[3] In 1998, in a leveraged buyout, the company was acquired by Trinity Acquisition on behalf of Kohlberg Kravis Roberts,[3] and in 1999 the name Willis Group was adopted.

[3] In October 2008, Willis acquired Hilb, Rogal & Hobbs Co. (HRH), one of the largest insurance and risk management intermediaries in North America, for $2.1 billion.

[5] In 2015, the Court of Appeal of England and Wales held that the company was entitled to an interim injunction to prevent Jardine Lloyd Thompson (JLT), a competing firm of brokers, from unfairly recruiting its remaining staff after more than 20 employees, including nearly all senior staff in one department, left Willis to work for JLT.