The Heroes actress will play Queen Eva in flashback sequences, TV Guide reports.
Sofer's episode will also feature Wizards of Waverly Place child star Bailee Madison as young Snow White - Ginnifer Goodwin plays the adult version of the fairytale icon on ABC's drama.
The instalment is set to air in early March - 44-year-old Sofer's recent acting credits include guest stints on Beauty and the Beast, Covert Affairs and House. She previously played recurring roles on Heroes and 24.
Downton Abbey star Lesley Nicol, The Walking Dead's Sonequa Martin-Green and Charmed star Rose McGowan have also signed up for roles on Once Upon a Time.
The ABC fantasy drama airs on Sundays at 8/7c on ABC and will return to Channel 5 in the UK later this year.
> Once Upon a Time: Ethan Embry joins cast, Julian Morris returns
Watch a promo for the next Once Upon a Time below: