Bump!
Trailer is still ways off, and season 1 is still filming. Nevertheless I thought it would be a good idea to update this thread and list the complete cast for season 1. There are still some roles to be filled, but most of season 1 is cast.
There is also some rumors that Netflix has already greenlit season 2 and 3, without even seeing any footage. If that's true, they must have faith that this can become a smash hit.
So, here is complete cast of season 1:
Henry Cavill - Geralt of Rivia
Freya Allan - Cirilla
Joey Batey - Jaskier/ Dandelion in English translation of the book, and in Witcher games
Millie Brady - Princess Renfri
Anya Chalotra - Yennefer of Vengerberg
Anna Shaffer - Triss Merigold
MyAnna Buring - Tissaia De Vries
Mimi Ndiveni - Fringilla Vigo
Therica Wilson-Read - Sabrina Glevissig
Tom Canton - Filavandrel
Imogen Daines - Danica
Eamon Farren - Cahir
Jodi May - Queen Calanthe
Björn Haraldsson - Eist
Adam Levy - Mousesack/ Ermion in Witcher 3
Lars Mikkelsen - Stregobor
Maciej Musial - Sir Lazlo
Royce Pierreson - Istredd
Wilson Radjou-Pujalte - Dara
Amit Shah - Torque
Natasha Culzac - Toruviel
Not naming the extras, but here you go.