Salma bint Hizab al-Oteibi won a seat in Mecca province in Saturday's vote, the electoral commission said.
Votes are still being counted in the municipal elections, which were the first where women could vote and stand as candidates.
A total of 978 women registered as candidates, alongside 5,938 men.
Officials said about 130,000 women had registered to vote in Saturday's poll, compared with 1.35 million men.
The vote is being seen as a milestone in the conservative kingdom, which is the only nation where women are not allowed to drive.
Female candidates had to speak behind a partition while campaigning or be represented by a man. Turnout was high, state media reported.
Elections themselves are a rare thing in the Saudi kingdom - Saturday was only the third time in history that Saudis had gone to the polls.
There were no elections in the 40 years between 1965 and 2005.
The decision to allow women to take part was taken by the late King Abdullah and is seen as a key part of his legacy.
In announcing the reforms, King Abdullah said women in Saudi Arabia "have demonstrated positions that expressed correct opinions and advice".
Before he died in January, he appointed 30 women to the country's top advisory Shura Council.
There were 2,100 council seats available in Saturday's vote. An additional 1,050 seats are appointed with approval from the king.