Saudi Arabia's King Abdullah has appointed 30 women to the previously all-male consultative Shura Council.
Two decrees reconstituted the council, which advises the government on new legislation, for a new four-year term - and stated that women should always hold at least a fifth of its 150 seats.
The king took the decisions following consultations with religious leaders.
The council has had female "advisers", but women still have little role in public life in the conservative state.
They are forbidden from driving, are currently excluded from holding high political office, and will get the vote for the first time in 2014. They are also unable to travel without permission from a male guardian and may not mix with unrelated men.
King Abdullah first announced that he was planning to name women to the Shura Council in 2011, when he also said they would be allowed to vote and stand as candidates in the 2015 municipal elections.
One of the royal decrees published on Friday by the official Saudi Press Agency (SPA) amended an article in the Shura Council's statute to guarantee women representation on the body, while the other named the 150 members, among them 30 women.
The king said he had consulted religious scholars, who had approved the participation of women in accordance with Sharia (Islamic law).
"Women... will enjoy full rights of membership, be committed to their duties, responsibilities and assume their jobs," he added.
The first decree also stated that special seating would be allocated for women inside the Shura Council building, and that a special entrance and exit would be built to ensure segregation of male and female members.
Two of the women appointed are princesses. One is the daughter of the late King Faisal; the other is the daughter of the late King Khaled.
The council will also have four Shia members, one of whom is a woman. This represents an increase of one seat for the minority community, which makes up about 10% of the population.
Jeddah-based journalist Maha Akeel described the announcement as "a very big step forward".
She told the BBC that the women on the Shura Council would be "under pressure from conservative elements" within the kingdom, but she was confident they would be more than able to defend themselves.
However, there was a sense of disappointment on social networking websites, with users expecting little change from previous councils. On Twitter, people began using the hashtag "#The_new_Shura_Council_does_not_represent_me".
Ms Akeel said that while she could understand their frustration, young Saudis needed to be "more realistic, more optimistic".
"These women will bring fresh energy and insights to the council. Their participation will open doors for women," she added.
The announcement comes two days after the Saudi authorities controversially beheaded a Sri Lankan domestic worker convicted of killing a baby in her care.
On Friday, the UN High Commissioner for Human Rights expressed her deep dismay at the execution, and said she was deeply troubled by reports of irregularities in Rizana Nafeek's detention and trial. Her birth certificate also allegedly showed she was a minor when the baby died.
The commissioner expressed concern at the sharp increase in executions in Saudi Arabia in recent years, rising to 79 in 2012 from 27 in 2010.