The quota will apply to more than 100 listed companies. Another 3,500 firms will be required to set targets to raise the number of female directors and women in other leadership positions.
A recent study released by the German Institute for Economic Research found that, last year, women accounted for 18.6 per cent of the supervisory board members the German equivalent of directors at the country's biggest 100 companies.
Lawmakers from Chancellor Angela Merkel's governing coalition of conservatives and Social Democrats backed the legislation today. Opposition lawmakers who argued that it didn't go far enough abstained.
"A real quota for women must apply to all companies," said Caren Lay, a lawmaker with the opposition Left Party.
The new quota won't apply to the management boards of the biggest companies or to public-sector employees, though officials are pledging to increase the number of women in public-sector leadership jobs.
Starting next year, companies that haven't met the quota would either have to appoint a woman to fill a vacancy, or leave the seat empty.
Schwesig said that is an effective measure because it would affect the balance of power on supervisory boards. In Germany, those boards normally contain equal numbers of employer and employee representatives.
Norway, Spain and France among others already have quota requirements.
