Slow Horses Season 6 Cast: Every Returning and New Character

Slow Horses Season 6 brings Gary Oldman’s Jackson Lamb back with the core Slough House team, several important MI5 figures and two especially notable additions. Apple confirms that Olivia Cooke returns as Sid Baker, while BAFTA winner Lenny Rush joins the ensemble.

The six-episode season begins September 16, 2026 and adapts Joe Country and Slough House. Apple’s official announcement lists the returning ensemble, although it does not map every actor to a Season 6 role on that page.

Premiere: September 16, 2026
Episodes: Six
New addition: Lenny Rush
Major return: Olivia Cooke as Sid Baker

Slow Horses Season 6 returning cast

Jackson Lamb, played by Gary Oldman

Gary Oldman as Jackson Lamb in Slow Horses Season 6 — Gary Oldman as Jackson Lamb. Image: Apple

Lamb remains the brilliant, abrasive head of Slough House as his agents are forced to run.

Don’t miss the best of The Mac Observer

Set us as a preferred source and our Apple reporting ranks higher in your Google Search results and Discover feed — one tap, no account changes.

Add as a preferred
source on Google

Or get it by email

River Cartwright, played by Jack Lowden

Jack Lowden as River Cartwright in Slow Horses Season 6 — Jack Lowden as River Cartwright. Image: Apple

River returns, with Apple’s images showing him alongside Lamb and the returning Sid Baker.

Diana Taverner, played by Kristin Scott Thomas

Kristin Scott Thomas as Diana Taverner in Slow Horses Season 6 — Kristin Scott Thomas as Diana Taverner. Image: Apple

Apple says Taverner pulls the team into a dangerous game of retaliation and revenge.

Catherine Standish, played by Saskia Reeves

Saskia Reeves as Catherine Standish in Slow Horses Season 6 — Saskia Reeves as Catherine Standish. Image: Apple

Standish returns as one of Lamb’s most experienced and dependable colleagues.

Louisa Guy, played by Rosalind Eleazar

Rosalind Eleazar as Louisa Guy in Slow Horses — Rosalind Eleazar as Louisa Guy with Jack Lowden. Image: Apple

Louisa remains part of the team facing the new threat.

Roddy Ho, played by Christopher Chung

Christopher Chung and Lenny Rush in Slow Horses Season 6 — Christopher Chung and Lenny Rush. Image: Apple

Apple’s Season 6 gallery pairs Roddy with Rush’s new character.

Shirley Dander, played by Aimee-Ffion Edwards

Aimee-Ffion Edwards and Tom Brooke in Slow Horses Season 6 — Aimee-Ffion Edwards and Tom Brooke. Image: Apple

Shirley returns to Slough House for the retaliation story.

J.K. Coe, played by Tom Brooke

Tom Brooke and Aimee-Ffion Edwards in Slow Horses Season 6 — Tom Brooke and Aimee-Ffion Edwards. Image: Apple

Coe is back with the agents after joining the team in an earlier season.

Sid Baker, played by Olivia Cooke

Olivia Cooke as Sid Baker with Jack Lowden in Slow Horses Season 6 — Olivia Cooke as Sid Baker with Jack Lowden. Image: Apple

Cooke’s confirmed return ends years of uncertainty, but Apple has not explained Sid’s absence.

Frank Harkness, played by Hugo Weaving

Hugo Weaving as Frank Harkness in Slow Horses — Hugo Weaving as Frank Harkness with Jack Lowden. Image: Apple

Weaving returns after Frank’s personal connection to River reshaped the story.

David Cartwright, played by Jonathan Pryce

Jonathan Pryce as David Cartwright in Slow Horses — Jonathan Pryce as David Cartwright. Image: Apple

River’s grandfather remains part of Apple’s announced ensemble.

New and additional Season 6 cast

Reece Nesmith, played by Lenny Rush

Lenny Rush and Christopher Chung in Slow Horses Season 6 — Lenny Rush and Christopher Chung. Image: Apple

Apple confirms Rush’s casting; advance reviews identify him as eyewitness Reece Nesmith.

Moira Tregorian, played by Joanna Scanlan

Joanna Scanlan as Moira Tregorian in Slow Horses — Joanna Scanlan as Moira Tregorian. Image: Apple

Scanlan is included in Apple’s confirmed Season 6 ensemble.

Peter Judd, played by Samuel West

Official Slow Horses Season 6 production still — Apple lists Samuel West in Season 6 but has not published an individual Peter Judd still. Image: Apple

West returns as political operator Peter Judd.

Emma Flyte, played by Ruth Bradley

Ruth Bradley as Emma Flyte in Slow Horses — Ruth Bradley as Emma Flyte. Image: Apple

Bradley is also listed in Apple’s returning cast.

Readers can review the confirmed release and cast details, the trailer’s major returns and our Season 6 review roundup. Which character are you most excited to see again? Let us know in the comments.

Apple’s list confirms participation, not the amount of screen time each performer receives. Since the season compresses two novels into six episodes, some familiar figures may support the central operation while others carry separate parts of the revenge story. Official episode credits will provide the final answer once each installment is released.