The report said current working practices in financial services do not support female success, with a culture of long hours disadvantaging those who wish to work more flexibly to combine home and work responsibilities.
"Firms with less diverse management teams are less able to see issues from many angles. This is especially important for a sector that has recently suffered scandals attributed to unchallenged leadership and 'groupthink'," said Michelle Daisley, partner at Oliver Wyman.
Last month regulators fined six major banks a total of $4.3 billion for failing to stop traders from trying to manipulate the foreign exchange market.
Just 4 percent of financial industry CEOs are women and more than a third of executive committees (ExCos) are still entirely male, according to the global study of more than 150 firms released on Thursday.
"The pace of change is too slow," Daisley said.
The report, Women in Financial Services, said in 2013 one in five board members of financial firms were female, up by two-thirds over the last decade.
But in ExCos, the group of executives sitting below board level, the pace of increase was slower. Only 8 percent of chief financial officers and 4 percent of chief risk officers were women.
In Sweden, women make up 35 percent of supervisory boards and 29 percent of executive management teams. Under Norwegian law, 40 percent of supervisory board members must be women.