King Hamad issued a decree on Tuesday appointing Muna Jassim al-Kawari to the civil courts.
Kawari said after her appointment: "I am very proud to be the first woman judge in Bahrain.
"This nomination does not surprise me though because his majesty has been encouraging women since the launch of reforms."
Two women are ministers in the Bahraini government.
A referendum in 2001 on turning the small Gulf state into a constitutional monarchy was the first time that women could vote.
Thirty-one women stood as candidates in municipal and parliamentary elections the following year, but none was elected.
The next round of elections is tentatively expected in October, but no date has been formally set.