After nearly three decades of working at the world's largest accounting firm, Cathy Engelbert is set to become Deloitte's chief executive in the United States, making her the first woman to lead any of the country's big professional services firms.

While many of these companies have intensified their efforts to recruit and retain female employees, and have in some cases even led the way on gender diversity research, their industries have still been slow to move the needle on women's representation in leadership. More than 60 percent of U.S. accountants and auditors are women, yet women comprise only about 18 percent of equity partners at the large firms, according to a 2010 study by Public Accounting Report.

In another study of these firms -- known as the "Big Four": Deloitte, Ernst & Young, PricewaterhouseCoopers and KPMG — senior women also reported less overall workplace satisfaction than senior men did. This was particularly true concerning promotions and compensation.

"Accounting firms are set up differently than corporations — with a partnership structure that has age-related tenure limits, resulting in an ‘up or out culture,’" Jan Combopiano wrote in an e-mail. She is the vice president and chief knowledge officer at Catalyst, a nonprofit organization that studies women's representation in business.  "This hinders women because they have such a limited time for advancement, during the very same time in their lives that they are starting families." Though Combopiano added, "But we are seeing accounting firms make efforts to create more inclusive workplaces."

While Deloitte's percentage of female partners is not significantly higher than that of other top firms, the company has been the first to break several high-profile diversity barriers in the past, such as appointing a female board chairman and a minority CEO.

Engelbert rose through the ranks of Deloitte as an accountant, though she will now oversee its portfolio subsidiaries, which employ roughly 65,000 people who focus on consulting and tax services as well as auditing and accounting. This U.S. arm of Deloitte reported nearly $15 billion in revenue for fiscal year 2014, marking several years of growth.

Like many such firms, Deloitte holds elections for its CEO and chairman roles every four years. After being selected by the board's nominating committee, the candidates then needs to garner at least two-thirds approval among Deloitte's voting partners and principals. Meaning that when Engelbert officially assumes her role on March 11, she presumably does so with a strong level of institutional support.

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