The 32-year-old, who plays Finnick Odair in the dystopian film series, said he felt “privileged” to appear in the BBC One show.
Cillian Murphy, 42, reprises his lead role as mob boss and tortured soul Thomas Shelby in the new series of the gangster drama which will be set in Birmingham before the Second World War.
He will be joined by Claflin, as well as Brian Gleeson, Anya Taylor-Joy, Neil Maskell, Kate Dickie, Cosmo Jarvis and Emmett J Scanlan - who will all debut in this season of the Bafta award-winning drama.
Helen McCrory, Paul Anderson, Sophie Rundle, Finn Cole, Kate Phillips and Natasha O’Keefe also return to the series.
BBC One boss Charlotte Moore announced in August that Peaky Blinders would move from BBC Two to BBC One after its fourth series attracted an average consolidated audience of 3.3 million viewers.
Claflin said: “From Steven Knight’s writing to the consistently brilliant production, I couldn’t feel more privileged to be invited to join this iconic show.”
Taylor-Joy said: “I could not possibly be more excited to be joining such a talented group of people. I can’t wait to get in and play this character.”
Gleeson said: “Looking forward to kicking around in the mud of Northern England with an exceptional cast and crew.
“The scripts are wild and pertinent - a classic Peaky brew.”
Series five of Steven Knight’s crime family saga sees the Shelbys thrown into difficult times following the financial crash of 1929.
Now the Labour MP for Small Heath in Birmingham, Shelby is approached by a politician with a plan that could change his and his family’s lives.
The fifth series will be directed by Anthony Byrne, whose previous work includes In Darkness, Butterfly and Ripper Street.