Tripplehorn will join the CBS drama as a new regular for season eight, replacing the outgoing Paget Brewster (Emily Prentiss).
The Big Love actress will play FBI linguistics expert Alex Blake, who has a past connection with Reid (Matthew Gray Gubler), TV Guide reports.
"People like Reid learned from [her]," executive producer Erica Messer revealed. "She is also a professor at Georgetown and Reid has guest-lectured at her forensic linguistics class before."
Messer also ruled out Blake becoming romantically involved with any of the existing BAU team members, explaining that the character is "in a relationship".
"When you get your heroes involved romantically, it just changes the show so much," she explained. "I feel pretty strongly about that as a rule."
Criminal Minds star Kirsten Vangsness (Penelope Garcia) recently told Digital Spy that she is looking forward to working with Tripplehorn, adding that she enjoys the star's work "a great deal".
> Matthew Gray Gubler signs two-year deal with Criminal Minds
Watch Digital Spy's full interview with Kirsten Vangsness below: