The 37-year-old actress, who has played Beckett in the crime series since its 2009 premiere, will not return for the planned ninth season after ABC decided not to renew her contract for "budgetary reasons", reported Deadline.
Her co-star Nathan Fillion, 45, who plays Beckett's husband Rick Castle, is expected to return for season nine if it is renewed for a shorter 13-episode run.
Katic did not comment on the reasons for her departure, but said, "Rather than distract from what was an amazing experience, I would just like to say that I'm very grateful to ABC for giving me the opportunity to be a part of a much beloved show. Thank you to the fans."
ABC said in a statement, "Kate Beckett has been a beloved character on our hit series 'Castle' for the past eight years. We are grateful for Stana Katic's talent and dedication to the series and we hope to continue our relationship. Tamala Jones has also been an integral part of the series and we are grateful she was a part of 'Castle'.