The bill is a response to a public outcry against a recent spike in incidents of rape of women and children in the country and growing demands for effectively curbing the crime.
The bill was passed by the National Assembly of Pakistan on November 17.
Islamabad, Pakistan: Sex offenders convicted of multiple rapes could face chemical castration in Pakistan after lawmakers on Wednesday passed new anti-rape legislation that aims to speed up convictions and impose tougher sentences.
It comes in response to a mass public outcry over a recent surge in rapes against women and children in the country, and growing demands to ensure justice for victims of sexual assault.
The bill states that Pakistan's government must establish special courts nationwide to expedite rape trials and ensure sexual abuse cases are decided "expeditiously, preferably within four months."
Those found guilty of gang rape will be sentenced to death or life in prison.
Chemical castration is the use of drugs to reduce libido or sexual activity. It is a legal form of punishment in countries including South Korea, Poland, the Czech Republic and in some US states.
Amnesty International said the penalty of chemical castration was "cruel and inhuman" in a statement last December, when the bill was announced.
"Instead of trying to deflect attention, the authorities should focus on the crucial work of reforms that will address the root causes of sexual violence and give survivors the justice they deserve," Amnesty said.
Fewer than 3% of sexual assault or rape cases result in a conviction in Pakistan, Reuters reported last December, citing Karachi-based non-profit War Against Rape.
In a landmark ruling in January, virginity tests on sexual assault survivors were outlawed in Pakistan's most populous province, Punjab.
The so-called virginity tests, which include inspecting the hymen or inserting two fingers into the vagina, are invasive examinations conducted under the belief that they can determine whether a female is a virgin.