The move was welcomed by activists who have called for greater rights for women in the kingdom, which enforces a strict version of Sunni Islamic law.
The king said the changes will occur after municipal polls on Thursday.
He made the announcement in a speech at the opening of the new term of the Shura Council – the formal body advising the king, whose members are all appointed.
Saudi Arabia is a conservative society which has been inching towards reform under the leadership of king Abdullah.
About 10 years ago the king said women should be central to the Saudi economy.
Since then, change has been gradual for fear of a religious backlash.
Steps have been taken to reduce segregation and give more respect to women.