Iraqi police identified the victim as Lamia Abid Khadawi, a member of caretaker Prime Minister Iyad Allawi's political party.
The attack on Wednesday occurred in front of her home in eastern Baghdad.
She is thought to be the first person in the 275-member National Assembly to be killed. The assembly was formed after elections on 30 January this year.
Armed men have targeted politicians in the past.
A former head of the Iraqi Governing Council, the predecessor to the interim government, was assassinated in a car bombing in May 2004.
Earlier this month, Allawi survived an assassination attempt when his convoy was attacked by a car bomber.
Iraq's parliament met for several hours earlier on Wednesday to discuss its rules and regulations and other issues.
It was also expected to vote on a proposed cabinet, the next step in the formation of a new government.
Allawi was the target of an
The parliament meets in the heavily fortified Green Zone in central Baghdad, and prominent lawmakers are often given police escorts around the capital to protect them against assassination attempts.
Khadawi was one of about 90 women elected to the assembly in January. By law, a third of the candidates on party lists had to be women.
In other developments, an Iraqi police officer was killed and three were wounded when a bomb detonated in Samarra on Wednesday, Aljazeera has learned.
The vehicle carrying the police officers was destroyed in the explosion.
In the southern city of Basra, a police officer was killed when men armed with machine guns shot at a police patrol.