The measure, announced several weeks ago, was approved Friday by the standing committee of the National People's Congress, government news agency Xinhua reported. It is expected to take effect early next year.
Couples who come from one-child families will be allowed to have two children. China had already made some exceptions to the policy for ethnic minorities and farmers.
China has a population of 1.35 billion, the world's largest. The one-child policy was introduced in the late 1970s in an effort to curb its growth.
As a result, China has a rapidly aging population and one in which men outnumber women because of sex-selection abortions and couples who give up female children for adoption to try for a boy.