Can I rent a flat in Lisbon without a guarantor (fiador)?

Yes, but expect landlords to ask for something else instead. The most common is paying more months of rent upfront. Some landlords also accept other forms of guarantee; ask what they accept. Tips: • Show a clear proof of income: your employment contract and recent payslips help a lot. • Get everything in writing in the contract: what is deposit, what is advance rent, and when the deposit is returned. • Never pay before seeing the home and confirming who owns it. Newcomers are the favourite target of rental scams. See the guide "Renting a home in Portugal as a newcomer". This is general information, not legal advice.