Is it haram to rebel against a government?

The classical Sunni position

The Quran tells believers to "obey Allah and obey the Messenger and those in authority among you" (Quran 4:59). Based on this and many hadith, the mainstream Sunni position became: be patient with unjust rulers rather than take up arms against them.

• Patience: "Whoever notices something which he dislikes done by his ruler, then he should be patient" (Sahih al-Bukhari 7054).
• No sword: when asked whether they should overthrow bad rulers by the sword, the Prophet ﷺ said no, as long as they establish prayer, and told them to hate the wrong without withdrawing obedience (Sahih Muslim 1855).
• A very narrow exception: the Companions pledged not to fight the ruler "unless we noticed him having open Kufr (disbelief) for which we would have a proof" (Sahih al-Bukhari 7056). Even then, scholars required that rebellion not cause greater harm.

The reasoning was practical. Scholars had seen civil wars destroy lives, families and cities, and concluded that an unjust order was usually less harmful than violent chaos. Some early Muslims did rise against tyrants, and a minority of scholars allowed it, but the later Sunni mainstream settled on patience.

No obedience in sin

Obedience is never unconditional. The Prophet ﷺ said a Muslim must listen and obey "as long as his orders involve not one in disobedience (to Allah), but if an act of disobedience (to Allah) is imposed one should not listen to it or obey it" (Sahih al-Bukhari 7144). Refusing to sin isn't rebellion. You simply don't do the wrong thing, without turning to violence.

Speaking up is a virtue

Patience doesn't mean silence. The Prophet ﷺ called "a word of justice to an oppressive ruler" the best jihad (Sunan Abi Dawud 4344, graded sahih), and taught that sincere advice is owed to leaders too (Sahih Muslim 55). Honest criticism, delivered with wisdom, is part of a healthy society.

Democracies are different

In the USA, UK and Europe, changing the government peacefully is built into the system. Voting, writing to your representative, joining a peaceful march, signing petitions and going to court aren't rebellion. They're lawful ways of giving advice and seeking justice, and many scholars encourage Muslims to use them. See Can I vote in elections as a Muslim?

What remains forbidden is violence, sabotage and joining armed groups. Respect the law even when you disagree with it. See Do I have to follow the laws of my country as a Muslim?