My father lived in Portugal and died there. I am his sole heir, and my tax residence is in France. Am I liable for inheritance tax in France?

Yes. In the absence of a tax treaty between France and Portugal governing inheritance taxation, the French tax authorities will tax all assets located in France and abroad (Art. 750 ter 3° CGI). However, inheritance taxes paid abroad may be credited against the tax due in France (Art. 784 A CGI).