Before you start

A passport or ID card (required to register any SIM under Portuguese rules)
An unlocked phone (or an eSIM-compatible device for an eSIM)
For a postpaid contract: a NIF (tax number) and usually a Portuguese bank account for direct debit
A Portuguese address for a contract (prepaid needs no address)

Step-by-step

1
Pick prepaid vs contract
Prepaid (pre-pago) is the fast, no-commitment route for newcomers: top up as you go, no NIF or bank account needed. A postpaid contract (pos-pago) is cheaper per GB and can bundle home internet/TV, but generally requires a NIF and a Portuguese bank account for direct debit, so most people start prepaid and switch later.
OnlineWho: YouA few minutes to decide-
2
Buy a prepaid SIM or eSIM
Buy from a MEO, NOS, or Vodafone store, or budget brands Moche and Lyca, with your passport. SIMs are sold at the airport, carrier shops, FNAC/Worten, and many kiosks. Increasingly you can activate an eSIM straight from the carrier app or buy a travel eSIM (Holafly, Airalo) before you land so you arrive connected. Lycamobile is popular for cheap calls to non-EU countries.
In personWho: You (carrier store, airport kiosk, or app)Same day; 15-30 minutes in storePrepaid starter packs roughly EUR 10-15 with initial data
3
Register the SIM with your ID
Portuguese rules require SIMs to be registered to an identity, so the seller records your passport/ID at purchase. Keep some identification handy even for a cheap prepaid SIM. An unregistered or wrongly registered SIM can be deactivated.
In personWho: You (with the seller)Done at purchaseIncluded
4
Top up, or move to a contract once settled
Recharge prepaid via the carrier app, ATMs/Multibanco, MB WAY, supermarkets, or kiosks. Once you have a NIF and a Portuguese bank account, you can switch to a monthly plan - often bundled with fibre internet and TV - usually keeping your number via portability (portabilidade).
Mobile appWho: YouAnytime; number portability typically ~1 working dayPrepaid bundles ~EUR 10-15/month; contracts vary by bundle

Documents you’ll need

Passport or ID card (for SIM registration)
An unlocked or eSIM-compatible phone
NIF (Portuguese tax number) - for a postpaid contract
Portuguese bank account details (IBAN) - for contract direct debit
Proof of address - typically only for a contract, not prepaid

Things most newcomers don’t know

Start prepaid - a contract needs a NIF and a Portuguese bank account.

Prepaid SIMs need only your passport, while postpaid plans are usually set up on direct debit and ask for a NIF plus a local IBAN. New arrivals almost always go prepaid first, then switch once those are sorted.

Source: carrier onboarding consensus (MEO/NOS/Vodafone)

Every SIM must be registered to your ID.

Portuguese telecom rules require SIMs to be tied to an identity, so the shop records your passport at purchase and an unregistered SIM can be cut off - always carry ID even for a cheap prepaid.

Source: ANACOM / carrier practice

An eSIM can have you connected before you land.

MEO, NOS, and Vodafone increasingly support eSIM, and travel eSIMs (Airalo, Holafly) activate over the air - useful for data on arrival before you reach a store for a local SIM.

Source: carrier + provider consensus

Pick Lycamobile or Moche to keep costs down.

Lycamobile is a budget MVNO favoured for cheap international calls, and Moche is MEO's low-cost youth brand - both undercut the headline plans of the big three for light or cost-conscious users.

Source: provider/community consensus

Common mistakes to avoid

Expecting to sign a postpaid contract before you have a NIF and a Portuguese bank account
Buying a SIM without carrying ID for the mandatory registration
Letting a prepaid SIM sit unused for too long and losing the number to deactivation
Paying tourist-priced travel eSIM rates long-term instead of moving to a cheap local prepaid bundle