Jack Lowden in Slow Horses
Jack Lowden plays River Cartwright, the young MI5 officer whose disastrous start places him under Jackson Lamb’s supervision. He appears from Series 1 onwards. River gives the drama a restless forward motion: he wants useful work, hates being underestimated and repeatedly finds that doing something quickly is easier than understanding the situation properly.
Lowden makes that frustration physical without turning River into a permanently furious man. He can push through an instruction, then realise a moment too late what somebody else actually meant. His exchanges with Gary Oldman are especially effective when River tries to sound in control and Lamb refuses to recognise the performance.
The opening operation in Series 1, episode 1 introduces both sides of Lowden’s work: the concentration of an agent tracking a target and the humiliation of being judged afterwards. River has to remain believable as someone trained for this job even when his position within the Service becomes the source of the comedy.
What he has said about River
Speaking to TheWrap in December 2022, Lowden argued that Lamb would eventually miss having a capable employee to grind down, although he would never say so. He also described River’s return to Slough House after Series 1 as evidence that restoring a career requires more than a single heroic intervention.
That reading captures the imbalance between the two actors’ characters. River treats another assignment as a potential escape route; Lamb treats River’s ambition as something he can exploit. Lowden’s performance stays engaging because the desire to leave is so easy to understand, even when the audience enjoys the workplace he is trying to abandon.
Standout scenes: Series 4 spoilers
The Series 4 opening changes the emphasis when River discovers a crisis at his grandfather’s home. Lowden’s scenes with Jonathan Pryce ask for something less competitive than his exchanges with Lamb: affection, alarm and the difficulty of deciding how to help somebody who resists assistance.
The encounter with Frank Harkness in Series 4, episode 6 then places River opposite a different kind of authority. The revelation that Harkness is his father shifts a conversation about intelligence into a personal confrontation. Lowden has to keep River listening while the meaning of his own history changes around him.
Career highlights and awards
Lowden’s stage breakthrough came through the National Theatre of Scotland’s Black Watch. His later performance as Oswald in Richard Eyre’s revival of Ibsen’s Ghosts earned the 2014 Olivier Award for Best Actor in a Supporting Role and the Ian Charleson Award. The stage role offers another character caught in consequences that cannot be solved through confidence alone.
He played Nikolai Rostov in the BBC’s War & Peace (2016). The following year brought Collins, an RAF pilot in Christopher Nolan’s Dunkirk (2017), and the leading role of Morrissey in England Is Mine (2017). These credits move from a literary ensemble to a compressed wartime thriller and a portrait of a musician before fame.
In Calibre (2018), Lowden plays Vaughn, whose hunting trip becomes a frightening moral trap. His performance won the BAFTA Scotland award for Actor in Film in 2018. The importance of hesitation in that film makes it a strong choice for viewers interested in the moments when River’s quick decisions finally slow down.
His portrayal of Siegfried Sassoon in Terence Davies’s Benediction (released in the UK in 2022) brought another BAFTA Scotland acting award that year. The contrast with River is substantial: a historical poet’s interior life replaces an agent’s urgent problem-solving, with attention directed towards memory, expression and what remains unsaid.
Other specific roles include Lord Darnley in Mary Queen of Scots (2018), Zak in Fighting with My Family (2019), and Kenneth Noye in The Gold (2023). He also played Orestes opposite Kristin Scott Thomas in Electra at the Old Vic in 2014, an earlier collaboration with another member of the Slow Horses ensemble.
Where to watch next
Calibre is the clearest next step for a tense thriller built around an increasingly difficult choice. Benediction offers a slower, more reflective leading performance and a completely different relationship with language.
Dunkirk shows how much Lowden can communicate inside a tightly organised ensemble with relatively little dialogue. For a longer television role, choose War & Peace, where Nikolai Rostov’s place in family and military life provides an alternative to River’s uneasy bond with the intelligence establishment.
Questions and answers
Who plays River Cartwright in Slow Horses?
Jack Lowden plays River, the ambitious intelligence officer assigned to Jackson Lamb’s department after a failed operation.
Which character did Jack Lowden play in Dunkirk?
His role in Christopher Nolan’s 2017 film is Collins, one of the RAF pilots involved in the evacuation story.
Has Jack Lowden won an Olivier Award?
Yes. He won Best Actor in a Supporting Role in 2014 for playing Oswald in Richard Eyre’s production of Ghosts.