Is it haram to park in a disabled parking space?

Yes, parking in a disabled space without a valid permit is wrong in Islam. It takes a right that belongs to people who really need it, breaks a fair law and can cause real hardship. "Just two minutes" doesn't change that.

Why it matters in Islam

Disabled bays exist so that people who use wheelchairs, have chronic pain or struggle to walk can reach shops, mosques and hospitals. Taking that space, even briefly, may force someone to give up and go home. Islam takes other people's rights (huquq al-ibad) very seriously, and Allah doesn't simply wipe away a wrong done to a person until it is put right or forgiven.

إِنَّ ٱللَّهَ يَأْمُرُ بِٱلْعَدْلِ وَٱلْإِحْسَـٰنِ وَإِيتَآئِ ذِى ٱلْقُرْبَىٰ وَيَنْهَىٰ عَنِ ٱلْفَحْشَآءِ وَٱلْمُنكَرِ وَٱلْبَغْىِ "Indeed, Allah orders justice and good conduct and giving to relatives and forbids immorality and bad conduct and oppression." Quran 16:90

Think of your brother or sister

The Prophet ﷺ said: "None of you truly believes until he loves for his brother what he loves for himself" (Sahih al-Bukhari 13). Imagine it's your elderly mother, or you after an injury, circling the car park because the accessible bay is taken. He ﷺ also counted removing something harmful from the road as a branch of faith (Sahih Muslim 35). Blocking the road for someone who already finds it hard is the opposite of that.

It's also a fair law

In the UK, the EU and the USA, disabled bays are protected by law and backed by fines. Muslims living in these countries have agreed to keep laws that don't ask them to disobey Allah, and this one simply protects vulnerable people. See Do I have to follow the laws of my country as a Muslim?

Common situations

"I'll only be a minute." Still not allowed. A disabled driver may arrive in that minute.
Using a relative's Blue Badge or placard when they aren't in the car is misuse and often a crime. It's also a form of deception. See Is it haram to lie on government forms?
You have a valid permit (or you're driving the permit holder): then you're fully entitled to the space, with no guilt at all.
Parent-and-child bays are usually a store courtesy rather than law, but the same spirit applies: leave them for those they're meant for.
Outside the mosque on Jumu'ah: rushing to prayer is no excuse. Park legally and walk.

If you've done it before

Don't despair. Make sincere tawbah, resolve not to do it again, and pay any fine you received. If you know you blocked a specific person, a sincere apology is a beautiful way to put it right.

Key points

Using a disabled bay without a permit takes someone else's right.
Love for others what you love for yourself.
Misusing a relative's badge is deception and usually illegal.
With a valid permit, the space is yours to use freely.

Tip: If the car park is full, drop your passengers at the entrance and park further away. The extra steps may well count as good deeds when your intention is to respect others.