The release of the figures signals a change of emphasis for campaigners who, having focused on getting more women into boardrooms, are now seeking greater parity in executive positions.
The 30% Club also called for companies to be more aware that women structure their careers in a different way to men, often gaining broader experience along the way.
The group said it had surveyed companies across the FTSE-100 and FTSE-250 with a total of 450,000 employees.
It found that on average women make up 21% of those at executive committee level at FTSE-100 companies. A quarter of companies have 30% female representation at this rank.
Helena Morrissey, chief executive of Newton Investment Management and founder of the 30% Club said: "Men and women are different - equally intelligent but we behave differently and are motivated by different things.
"This new research gives more depth to the intuitive argument that balanced teams perform better, and gives companies specific actionable ideas to improve their management of all talent - regardless of gender."
The group was launched three years ago and signed up a number of company chairmen to their aim for 30% of board positions to be filled by women.
This has been supported by a Government target for 25% of FTSE 100 directors to be female by 2015. There has been progress towards this aim with women now making up 19% of FTSE-100 directors, up from 12.5% three years ago.
But while there are more female non-executive directors, very few top-level executive positions are held by women. Katherine Garrett-Cox of Dundee-based Alliance Trust, is a rare female chief executive.
The group concluded that women tend not to show the same level of ambition as men early in their careers but this increases as they climb the ladder. This means that companies should reassess career options for women, particularly when male peers are more overt about their aspirations, it said.
The group also found that women often make more side-ways career moves than men over the same time span with a mid-life career surge. This, it concluded, can result in senior female executives having broader experience than male ones.
There are also differences in how men and women are perceived as leaders. Women are more frequently described as providing values-based leadership while men are rated more frequently for their commercial acumen and rational approach to problem-solving.