APCO

Margery Kraus founded APCO Associates in 1984 as a subsidiary to Arnold & Porter, one of Washington's largest law firms, and from where APCO's name is derived. Grey Global Group, a New York–based global advertising and marketing agency, purchased majority ownership of APCO in 1991 from Arnold & Porter. On September 28, 2004, APCO announced its independent buyout from Grey Global and has thus become one of the largest privately owned public relations firms in the world.

In 2016, Kraus stepped down from her role as CEO, for the role to be filled by Brad Staples, who is a member of the London office. When speaking to PR Week, Staples announced a company-wide effort to centralize global account leadership, shifting some manage roles to Europe, rather than the United States.

In February 2020, APCO Worldwide announced an agreement to a partnership with Erie Street, a Chicago-based advisory firm. APCO declined to disclose financial terms but has confirmed that the partnership will not affect ownership or staffing at either firm.

In 2023, APCO Worldwide acquired Gagen MacDonald, a Chicago-based employee engagement firm Camarco, a London-based financial communications consultancy, and NGC International Advisory, a Dubai based public policy and government affairs consultancy led by Mohamed Bahaa.