The actor is the latest big name to be cast opposite lead actor Cillian Murphy in the Tom Harper-directed film. Last month it was revealed that Rebecca Ferguson (Silo) is also on board. As with Ferguson, details of Keoghan's (pictured) role are being kept secret.
As previously reported, Netflix greenlit the Peaky Blinders film in June, starring Oscar winner Murphy in a return to the iconic role of Tommy Shelby, leader of the Birmingham gangster family of the same name.
The epic continuation of the multi-award winning saga is written by series creator Steven Knight. He will produce alongside Caryn Mandabach, Murphy and Guy Heeley.
Executive producers are Harper, David Kosse, Jamie Glazebrook, Andrew Warren and David Mason. The film is made in collaboration with BBC Film.
While plot details are not yet known, Knight has previously said the story will take place during World War II. Production is expected to begin this year.
Keoghan, who received an Oscar nomination for Best Supporting Actor and won the BAFTA in that category for Martin McDonagh's 2022 hit The Banshees of Inisherin, starred in Emerald Fennell's Saltburn last year, for which he received BAFTA and Golden Globe nominations and co-starred with Murphy in the awards season.
In television, Keoghan has appeared in Apple TV+'s limited war series Masters of the Air, HBO's limited historical drama series Chernobyl and Netflix's crime series Top Boy.