Do I lower my US, UK or other income tax liabilities if I retire or work in Portugal?

If you move your residency to Portugal, under Portuguese law you are liable to pay taxes in Portugal. Portugal has signed treaties to prevent double taxation with 71 countries (including most European Countries, United States and Canada) that assure its citizens and residents the protection against being taxed in more than one country.
 
If you move your residency to Portugal you may be entitled to benefit from the Non Habitual Resident Regime that allows you to obtain tax...

If you move your residency to Portugal, under Portuguese law you are liable to pay taxes in Portugal. Portugal has signed treaties to prevent double taxation with 71 countries (including most European Countries, United States and Canada) that assure its citizens and residents the protection against being taxed in more than one country.
 
If you move your residency to Portugal you may be entitled to benefit from the Non Habitual Resident Regime that allows you to obtain tax exemptions on several types of income earned aboard such as pension income, dividends, interests, etc.
 
I cannot expand on the Foreign Earned Income Exclusion available to US taxpayers as I am not expert in US tax regulations.  If you are a US taxpayer I recommend that you ask your tax expert about the Foreign Earned Income Exclusion, and how it could be combined with the Portuguese Non Habitual Resident Regime in order to give you the best outcome.

 

(View of the rooftops and the  seaside from The Blue Boutique Hostel and Suites, Estoril, Portugal, pictured.)