If you remain a French tax resident, then yes, your Spanish property comes into some of your obligations in France, even though it is taxed first in Spain. The good news: the France-Spain tax treaty prevents you being taxed twice. Here is what you need to know, to be confirmed with your adviser for your situation.
If you do not let the property
In Spain, you declare a deemed income for the second home every year, as explained in our article on annual taxes. In France, a property you use yourself does not generate income to declare for income tax.
If you let it
Rent is taxable in Spain, where the property is located. You must also declare it in France, on the foreign income return (form 2047) and then on your main return. France then grants a tax credit that cancels out the double taxation, but this income can affect the rate applied to your other income. The question of French social charges is worth checking with an adviser.
Your Spanish bank account
Every account opened abroad must be declared to the French tax authorities each year, using form 3916, attached to your income tax return. Forgetting is penalised with a fine, even if the account is only used to pay the house bills.
IFI (French property wealth tax)
If your net property assets exceed the threshold for the French property wealth tax, your Spanish property is counted along with your French properties.
When you sell
The capital gain is taxed in Spain, with 3% of the price withheld by the buyer if you are not a Spanish resident. It is also declared in France, where the treaty provides a mechanism to avoid double taxation.
None of this is complicated, as long as you know from the start. An accountant or gestoría used to French owners handles these returns every year for a modest fee.
