If you are a resident in Portugal and holder of a driver’s license issued by another country, at some point you have to swap your old license for a Portuguese one. Timing and process depend on where your license was issued.
IMT I.P. (Instituto da Mobilidade e dos Transportes) have detailed instructions in English online. As rules seem to be changing frequently lately, best look for the latest info here:
http://www.imtonline.pt/index.php/troca-de-titulos-conducao-estrangeiros/driving-licence-exchange109
The process is different depending on where your current license was issued.
EU: You can drive in Portugal on an EU driving licence until it expires.You must register your address in Portugal with IMT services within 60 days of settling in Portugal.There is no charge for this service.
Full details including documents to be submitted and fees at http://www.imtonline.pt/index.php/troca-de-titulos-conducao-estrangeiros/driving-licence-exchange109/9-uncategorised/487-1st-situation-17
UK and other countries covered by international traffic conventions: You can drive in Portugal, as a tourist, with a driving licence issued by a country covered by the agreements mentioned above, for a period of 185 days following your entry into Portugal and providing you are not intending to settle.
If you take up residence in Portugal, you must take into account the following deadlines, which are effective from the date on which your residence document is issued:
– Up to 90 days. You can continue to drive on a licence issued by a country mentioned above for up to 90 days from the date of issue of your residence document, but you must apply to IMT for an exchange during this period.
– From 90 days up to 2 years. You can no longer drive on a licence issued by a country mentioned above, but you can still apply to IMT for an exchange during this period
– After 2 years. You can apply for the exchange of your licence, but you will have to pass a practical driving test
Full details and link to countries to which this applies http://www.imtonline.pt/index.php/troca-de-titulos-conducao-estrangeiros/driving-licence-exchange109/9-uncategorised/484-2nd-situation-17
There’s also this document specifically for UK licenses in view of Brexit http://www.imt-ip.pt/sites/IMTT/Portugues/Noticias/Documents/2019/Noticia-Brexit-Cartas%20de%20Condu%C3%A7%C3%A3o-Driving%20Licences/FAQ%27s%20-%20Brexit%20%20ENG%20v2.pdf
Other countries:
Special categories
If your license includes heavy vehicles or large trailers, you will have to take a “CAP” (psychological suitability test that I gather mainly checks reflexes) and submit the certificate with your application. However, there have been instances where people have been denied the additional categories despite having done the CAP. This seems to relate to whether a specific test was passed to obtain those categories, i.e. older licenses that included other categories after having passed merely a test for passenger cars appear to lose the extra categories upon exchange. The water is muddy on this, so investigate in good time.