Thorne-Smith first joined the show last year and appeared in a number of episodes as Lyndsey, a love interest for Alan (Jon Cryer).
Her last episode aired in January.
Thorne-Smith has now signed up to return as a recurring character in the new season, Entertainment Weekly reports. However, details of her storyline have not yet been revealed.
Thorne-Smith has previously had roles in shows including According To Jim, Ally McBeal, Melrose Place and LA Law.
The news comes shortly after it emerged that Judy Greer has landed a recurring role in the upcoming season of Two and a Half Men.
The show, which will see Ashton Kutcher replacing former star Charlie Sheen, will return on September 19 on CBS.
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