For information about the portuguese tax system see: Portuguese Tax System.
Portugal has bilateral agreements with other States, including Ireland, to avoid double taxation of income – Double Taxation Agreements (DTA).
Before engaging in any professional activity a Taxpayer’s Card (Cartão de Contribuinte) is required. It can be obtained by presenting a valid identity document and submitting a registration form at your local Tax Office (Repartição de Finanças).
In the case of a resident in the Portuguese territory, IRS is levied on the overall income, including income from outside that territory.
For more information visit the Portuguese Tax System.