The Refugees - which will enter production this summer - is a co-production between BBC Worldwide and Atresmedia.
It is the first time BBC Worldwide have collaborated with a European broadcaster on a project.
Tena currently appears as Osha in HBO's Game of Thrones, and previously played Nymphadora Tonks in the Harry Potter film series.
The Refugees is an English-language sci-fi drama created by Ramón Campos, Gema R. Neira, Cristóbal Garrido and Adolfo Valor.
It explores the impact on a small rural community after millions of refugees from the future travel back in time to seek shelter in the present day.
The series will premiere on Spanish channel laSexta in the autumn, with BBC Worldwide serving as co-producer and commissioner for international channels, as well as global distributor.
Further casting announcements, including the appointment of a director,