[header] How to file taxes as a qualified widow or widower [title] Determine your previous filing status. [step] You must have qualified to file jointly before your spouse died, even if you chose to file separately. Anyone claiming the qualified widow (er) status must have also been able to file taxes jointly in the year of the spouse's death. 
[substeps] It doesn't matter if you actually did file jointly before the death of your spouse, just that you qualified to. The only requirement for filing a joint return is that you are legally married.