The Ugly Betty actress will play a recurring role on TNT's hit revival of the classic soap, according to TVLine.
Her character is being described as a controlling and manipulative older woman who will go to any lengths to protect her family.
63-year-old Light is best known for her television roles on ABC soap opera One Life to Live, ABC sitcom Who's the Boss? and NBC's Law & Order SVU.
The Walking Dead actress Emma Bell will also join Dallas for season two as "classic beauty" Emma, while Mitch Pileggi - who plays Harris Ryland, scheming ex-husband of Ann Ewing (Brenda Strong) - has been promoted to a series regular.
Dallas continues in the UK on Wednesdays nights on Channel 5 and will return to US screens on January 28.
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Watch the stars of Dallas talk to Digital Spy below: