Women still make up less than half of the executive committee roles at most large PR firms and only four women lead agencies with more than $100 million in global revenue.

PR agencies, which rely on strong talent to service clients, have long employed a predominately female workforce: a 2008 survey found that 70% of PRSA members were women while industry leaders estimate that women make up two-thirds of the industry's workforce.

Yet the number of women executives, including CEOs, at agencies ...