The 33-year-old actress announced on Twitter that she will join the fantasy drama's fourth season.
Pressman didn't disclose what role she will be playing, but instead left a cryptic written clue involving "extensions, eyelashes and gowns."
Season 4 will see the addition of characters from Disney's Frozen, including Elsa (Georgina Haig), Anna (Elizabeth Lail), Kristoff (Scott Michael Foster) and Prince Hans (Tyler Jacob Moore).
'Once Upon a Time' will return for its fourth season on September 28.