Dev Patel as Gawain

Alicia Vikander as Lady / Essel

Joel Edgerton as Lord

Sarita Choudhury as Mother

Sean Harris as King

Kate Dickie as Queen

Barry Keoghan as Scavenger

Erin Kellyman as Winifred

Ralph Ineson as Green Knight

Emilie Hetland as First Thief

Anthony Morris as Second Thief

Megan Tiernan as The Young Queen

Helena Browne as Sightless Woman

Brendan Conroy as Taverngoer

Chris McHallem as Lord in Waiting

Atheena Frizzell as Youngest Sister

Donncha Crowley as Bishop

Noelle Brown as Madam

Anaïs Rizzo as Helen

Joe Anderson as Paris

Nita Mishra as Older Sister

Tara Mae as Middle Sister

Sam Uppal Lynch as Prince Age 7

Adam Karim as Prince Age 17

Ruth Patel as Princess Age 4

Rose Patel as Princess Age 6

Emmet O'Brien as Magician

Andrea Deaskovic as Giant

Aoibheann Garry as Giant

Isabel Friosi as Giant

Hannah Sjoden as Giant

Lucy Waters as Giant

Melinda Dempsey as Giant

Rachel Quinn as Giant

Ethan Dillion as Soldier #1 (uncredited)

Aaron Edo as Soldier #2 (uncredited)

Youssef Quinn as Soldier #3 (uncredited)

Patrick Duffy as Gawain's Friend in Tavern (uncredited)

Janet Grene as Townsfolk (uncredited)

Tyrone Kearns as Noble (uncredited)

Tom Leavey as Knight of the Round Table (uncredited)

Stuart Mackey as Lancer (uncredited)

Aoife Gaffney as Girl at Round Table