Astier is most known as the creator, director, writer, editor, composer, and lead actor of the French television series Kaamelott, in which he also plays King Arthur.

His son Ethan plays Arthur's dream heir in Book V. Moreover, the mother of his first five children, Anne-Gaëlle Daval, is head of the costume designs on Kaamelott and the short film Dies Irae.

Passionate of technologies, he confirms in 2018 on twitter, that Kaamelott's film adaptation has been written with a bepo keyboard[5] on a raspberry pi, running Wordgrinder text-editor software.

In 2001, he was the co-screenwriter and the songwriter of the short movies Soyons sport and Un soupçon fondé sur quelque chose de gras.

He has the ambition to extend the TV show to the cinema as a trilogy, but not before 2012, since Alexandre Astier plans to work as a director on another movie before launching Kaamelott on the big screen.

In June 2010, invited on the set of the show "J'irai LOLer sur vos tombes", he unveiled his project to publish a series of graphic novels titled Kaamelott Resistance as a transition between the TV format and the future cinema films.