I am from the US.
Do you need an international drivers license to drive in Portugal?
You will find conflicting information and responses to your post. Whenever I drive overseas I get one-easy to get and cheap at AAA. I am of the school that says I’d rather have it and not need it than need it and not have it.
From the recent RS Forum discussions :https://community.ricksteves.com/travel-forum/ireland/two-more-questions-for-driving
An International Driver's Permit is not required in Portugal AFAIK, however it would be a good idea to have one anyway. Note that this is not a license per se, but rather a permit which must be used in conjunction with your home D.L. Given the small cost for an IDP, it makes sense to have one. This may be more crucial in the event you're involved in an MVI.