Ruling on rulers who do not judge by what Allah has revealed
Q: Are the rulers who judge by laws other than what Allah decreed considered Kafirs (disbelievers)?

And in case they can still be considered Muslims, how can we reconcile this with Allah's Saying: And whosoever does not judge by what Allâh has revealed, such are the Kâfirûn (i.e. disbelievers of a lesser degree as they do not act on Allâh’s Laws). ?
A: Those who judge by laws other than what Allah revealed vary according to their beliefs and deeds. Those who rule by secular laws believing that they are more appropriate and propitious than the revealed Laws of Allah are Kafirs (disbelievers) according to the unanimous view of Muslim scholars. The same ruling applies to those who rule by manmade laws instead of the Shari`ah (Islamic law) of Allah believing that it is permissible to do so, even if they still acknowledge that the Shari`ah is more superior than manmade laws. This is because they make lawful what Allah has prohibited.
Whoever judges by what Allah did not reveal on the ground of mere whimsical desires, or in the hope of earning some material gain, or due to hostility towards the defendant, or for any other reason while being fully aware that by doing so he is disobedient to Allah and that it is obligatory to rule by the Shari`ah, such a person is a grave sinner and has indeed fallen in minor Kufr (disbelief), Zhulm (injustice), and Fisq (flagrant violation of Islamic law). This ruling is reported from Ibn `Abbas (may Allah be pleased with them both), Tawus and a group of the Salaf (righteous predecessors). This was also the preponderant view of the majority of Muslim scholars. In the end, it is Allah Alone Who grants success.
Fatwa by: Shaykh Abdul-Aziz ibn Abdullah ibn Baz