Sébastien Mortamet is a French actor primarily known for his work in voice acting, particularly for the French dubbing of anime and other television series. He is a Lyonnais comedian who trained at the Conservatoire de Villeurbanne and actively works on a variety of projects, spanning classical theatre, contemporary creations, and voice-over work for films and animated series.

In the realm of anime, Mortamet is notably recognized for his role as the protagonist Keiichi Maebara in the French adaptations of the anime series When They Cry, specifically for the Rei and Kai seasons, which are also known under the French titles Hinamizawa, le village maudit. His other significant anime roles include lending his voice to Ittetsu Takeda in the popular sports anime Haikyu!! and to Chimada in Death Parade. He also contributed to the series Kimi ni Todoke, providing additional voices in its first season and voicing the character Kento Miura in the second season.

Beyond anime, his dubbing portfolio is diverse, encompassing work on live-action series and animated programs such as Black Mirror, Power Rangers, and Fangbone. In addition to his on-screen and voice dubbing work, Mortamet is also active as an audiobook narrator, having recorded titles for publishers like Lizzie.