Short answer
No. Representing someone in a dispute is a valid contract in Islamic law (wakalah bil-khusumah), and helping people get their rights is good work. It becomes haram when you knowingly argue for a false claim, help a client take what is not his, or work in areas built on haram, such as enforcing interest.
Acting as an advocate for a fee is permissible. It is haram to defend a claim you know is false, to hide the truth, or to draft and enforce contracts the Shariah forbids. A lawyer working under a non-Muslim legal system should choose work where the outcome he argues for is just.
The four schools agree on this.
Explanation
Justice is a command in Islam: "be persistently standing firm in justice" (4:135). A person who cannot argue his own case in court may appoint someone to do it for him, and all four schools accept this agency in litigation. A lawyer who protects tenants, victims, families, workers and businesses from injustice, and is paid for it, earns halal money.
The limit is set in the Quran: "do not be for the deceitful an advocate" (4:105). The Prophet ﷺ told people who brought disputes to him that one of them might argue more cleverly than the other, and that if he ruled for someone on the basis of that skill, what he gave him of his brother's right was a piece of the Fire. Winning a case does not make the result halal.
In practice:
- Allowed: civil and commercial disputes, immigration, employment, property, contracts, defending an accused person so that he gets a fair trial and no more than a just sentence.
- Not allowed: building a case on lies or false evidence, helping a client take what is not his, enforcing interest or drafting interest-based deals, helping split an estate in a way that cuts off heirs Allah named.
- Take care with family law, where you may be asked to secure more than the Shariah gives your client.
The same rules apply to a woman who practises law, with the usual rules of dress and of avoiding being alone with men she is not related to. See Are women allowed to work in Islam? and, for other careers, Which jobs are haram? Because each area of practice raises its own questions, a Muslim lawyer does well to keep a mufti he can ask.
Ask a mufti about your own case. This answer explains the general ruling. When the details of your situation matter, as they do here, ask a qualified mufti and give them the full facts. Where to ask a scholar.
The evidence
Quran, Surah An-Nisaa 4:105
إِنَّآ أَنزَلْنَآ إِلَيْكَ ٱلْكِتَٰبَ بِٱلْحَقِّ لِتَحْكُمَ بَيْنَ ٱلنَّاسِ بِمَآ أَرَىٰكَ ٱللَّهُ ۚ وَلَا تَكُن لِّلْخَآئِنِينَ خَصِيمًۭا ﴿١٠٥﴾
Indeed, We have revealed to you, [O Muhammad], the Book in truth so you may judge between the people by that which Allah has shown you. And do not be for the deceitful an advocate.
Arguing for a dishonest party is forbidden.
Quran, Surah An-Nisaa 4:135
۞ يَٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ كُونُوا۟ قَوَّٰمِينَ بِٱلْقِسْطِ شُهَدَآءَ لِلَّهِ وَلَوْ عَلَىٰٓ أَنفُسِكُمْ أَوِ ٱلْوَٰلِدَيْنِ وَٱلْأَقْرَبِينَ ۚ إِن يَكُنْ غَنِيًّا أَوْ فَقِيرًۭا فَٱللَّهُ أَوْلَىٰ بِهِمَا ۖ فَلَا تَتَّبِعُوا۟ ٱلْهَوَىٰٓ أَن تَعْدِلُوا۟ ۚ وَإِن تَلْوُۥٓا۟ أَوْ تُعْرِضُوا۟ فَإِنَّ ٱللَّهَ كَانَ بِمَا تَعْمَلُونَ خَبِيرًۭا ﴿١٣٥﴾
O you who have believed, be persistently standing firm in justice, witnesses for Allah, even if it be against yourselves or parents and relatives. Whether one is rich or poor, Allah is more worthy of both. So follow not [personal] inclination, lest you not be just. And if you distort [your testimony] or refuse [to give it], then indeed Allah is ever, with what you do, Acquainted.
Upholding justice is a duty, and helping people reach it is good work.
Sahih al-Bukhari 2680
Sahih... إنكم تختصمون إلي ولعل بعضكم ألحن بحجته ...
"You bring your disputes to me, and perhaps one of you is more eloquent in his argument than the other."
A ruling won by clever argument does not make another person's right lawful for you.
Where the ruling is recorded
- al-Hidaya, Kitab al-Wakala, chapter on agency in litigation and taking possession. Appointing an agent to argue one's case is valid.
- Radd al-Muhtar (Ibn Abidin), Kitab al-Wakala. The rules of agency in disputes and the agent's fee.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.