The news was announced in a cryptic teaser trailer, which followed Saturday’s season finale on BBC One.
The BBC says the Christmas special will “celebrate the gift of giving” and be told in an “innovative, format-breaking way”.
A teaser image for the trailer showed a hospital ward covered in snow, with a florescent jacket on the ground.
Casualty has been on British TV since 1986 and is the longest-running medical drama series in the world.
It follows the lives of staff and patients in the A&E ward of the fictional Holby City Hospital.
The show’s most recent season has been broken into four mini-series, Driving Force, A History Of Violence, Breaking Point and Storm Damage.
This season has also seen the departure of the show’s longest-serving character, Charlie Fairhead, played by Derek Thompson.
The series has won six Baftas and been nominated for 18. It is also nominated in the serial drama category of this year’s National Television Awards (NTAs).
Its spin-off series Holby City, which showed the lives and careers of those working on the surgical wards of the hospital, began in 1999 and was axed in 2021, with its final episode airing in 2022.
The most recent series of Casualty can be streamed on BBC iPlayer.
