Karin Huldt was born Karin Lovisa Huldt Björnberg on October 1, 1979, in Sweden. She graduated from Heleneholm Highschool, Malmö, Sweden, in 1999, majoring in drama. In 1998–2002, she attended Theater Academy in Malmö (1998–2002.) Huldt made her film debut in 1995, playing "Linnea" in Jan Linell's short film Som krossat glas i en hårt knuten hand, starring Thomaz Ransmyr and Carl-Johan Sundberg. The same year, she was also seen in Bo Widerberg's feature film Lust och fägring stor, starring Johan Widerberg and Marika Lagercrantz.

In 2002, Huldt portrayed "Jill" in SVT's TV series Cleo. In 2008, she played a patient in Sanna Lenken's short film Valborg with Emil Almén and Eva Fritjofson. Huldt has been active in, among others, Dramaten, Young Stage/ East, Halland's Music and Theater, Malmö City Theater, Skillinge Theater, and Västmanland's Theater.

She is also a ballet dancer and went to the Swedish Ballet School in Malmö.