Mercer has several distinct lines of business, namely: health and benefits, investments and retirement, workforce and careers, and M&A advisory services.

It is the world's largest investment advisory with over US$300 billion outsourced assets under management and US$16 trillion under advisement in total.

[11] Founded by organizational theorist David A. Nadler in 1980, Delta Consulting Group worked to structure effective executive teams.

[12][13] The firm had an influential client list, including corporations such as 3M, Citicorp, Procter & Gamble, The New York Times, and Xerox.

[16][17] The group grew through further acquisitions of Canadian Johnston Smith International, French Change Management Consultants, Spanish c.r.m.

[29] Also in 2010, Mercer acquired Brecksville, Ohio–based Innovative Process Administration LLC (IPA), a health benefits and technology provider.

[32] Also in 2013, Mercer acquired PricewaterhouseCoopers' pension windup (termination) administration business in Canada,[33] and Global Remuneration Solutions (GRS), a South African compensation and benefits survey data and rewards information provider.

[34] In 2014, Mercer acquired Norwell, Massachusetts–based Transition Assist, a private health care exchange specializing in coverage for Medicare-eligible retirees.

[35] Also in 2014, Mercer acquired Jeitosa Group International, a business and technology consultancy,[36] and a 34% stake in South Africa–based employee benefits specialist Alexander Forbes.

It acquired Hopkinton, Massachusetts–based Comptryx, a workforce metrics company offering surveying, modeling and analytics services,[40] and also acquired HRBS, a provider of career and talent consulting and information services to clients across Asia, particularly Hong Kong, Singapore and mainland China.