Production notes

The series was given a straight to series order by Apple TV+ in October 2019, with English writer and comedian Will Smith serving as showrunner. Each of the first five series has adapted the corresponding novel in the Slough House set. In October 2024, the show was renewed for a sixth series, which jointly adapts the sixth and seventh books, Joe Country and Slough House. The fifth series premiered on 24 September 2025, followed by new episodes on a weekly basis until the season finale on 29 October 2025. In July 2025, ahead of the fifth series premiere, Apple TV+ renewed for a seventh series which is to be based on Bad Actors. The sixth series premiered on 16 September 2026, with new episodes being released on a weekly basis until the finale on 21 October 2026. The day before the sixth series premiered, Apple TV renewed the show for an eighth series, based on the novel Clown Town. By 2025, the series began receiving praise for its production schedule, which allows it to release seasons yearly despite being a streaming series. The Wall Street Journal released an op-ed regarding the show's production schedule and strategy, which includes filming seasons back-to-back, and having multiple phases of production in motion at once. In July 2025, it was announced that Smith would depart as showrunner after the fifth series, with Gaby Chiappe taking over as head writer for the sixth series, and Ben Vanstone for the seventh and eighth. Smith described his departure as a "practical decision" in the face of difficulties managing scriptwriting for two series at a time, per the show's established schedule of simultaneously shooting one series while writing and pre-producing the next.

In October 2019, along with the series order, Gary Oldman was announced to star. The cast was rounded out in December 2020 with the additions of Olivia Cooke, Jonathan Pryce, Kristin Scott Thomas and Jack Lowden.

Since its premiere, production of Slow Horses has followed a schedule of shooting two series back to back, with the next series already having completed filming by the time the current one is released. Commentators have noted how the speed and consistency of Slow Horses' release schedule stands in contrast to the increasingly long, multi-year gaps between seasons of prestige TV shows, such as Severance and Stranger Things. Filming of the first series began on 30 November 2020 in the UK, and continued into February 2021. In July 2021, filming continued in Stroud, Gloucestershire. It was originally intended to film earlier in 2020 but was delayed due to the COVID-19 pandemic. By March 2023, filming for the third series had been completed and filming for the fourth was about to begin. In June 2025, Oldman announced that filming for the sixth series had already been completed prior to the release of the fifth, and that filming for the seventh was expected to begin by October of that year. Each series thus far has consisted of six episodes helmed by a single director: James Hawes directed the first series, Jeremy Lovering directed the second, Saul Metzstein directed the third and fifth, Adam Randall directed the fourth, sixth, and eighth, and Robert McKillop directed the seventh. The sixth series received a preview screening in the Primetime programme at the 2026 Toronto International Film Festival prior to its Apple TV release.

All six series of Slow Horses have received critical acclaim. For the first series, Rotten Tomatoes lists a 95% approval rating based on 60 reviews with an average rating of 7.5/10. The website's critical consensus reads, "Slow Horses refreshes the espionage genre by letting its band of snoops be bumbling, with Gary Oldman giving a masterclass in frumpy authority." On Metacritic, the first series has a weighted average score of 78 out of 100 based on 22 critics. The second series received a 100% approval rating on Rotten Tomatoes based on 25 reviews with an average rating of 8.5/10. The website's critical consensus says, "Slow Horses says nay to the sophomore jinx with a second series that might be even better than its supremely addictive predecessor." On Metacritic, series two has a weighted average score of 84 out of 100 based on 10 critics. Oldman was nominated for a Golden Globe and BAFTA Award for his portrayal of Jackson Lamb. The third series received a 98% approval rating from Rotten Tomatoes based on 43 reviews with an average rating of 8.5/10. The website's critical consensus reads, "Slow Horses' shabby charms reach a full gallop in this superb third season, yielding what might just be Slough House's most compelling operation yet." On Metacritic, series three has a weighted average score of 85 out of 100 based on 21 critics. The third series received nine Primetime Emmy Award nominations, including Lead Actor in a Drama Series for Gary Oldman, Supporting Actor in a Drama Series for Jack Lowden and Outstanding Drama Series. The fourth series received a 100% approval rating from Rotten Tomatoes based on reviews from 44 critics with an average rating of 8.6/10. The website's critical consensus says, "The stakes get more personal than ever before in Slow Horses' superb fourth season, proving that this spy series is saddled up for the long haul with no signs of fatigue." On Metacritic, series four has a weighted average score of 85 out of 100 based on 19 critics. Oldman was nominated for his second Golden Globe, second Emmy Award, second BAFTA Award, and first Screen Actors Guild Award for his performance. The fifth series has received a 96% approval rating from Rotten Tomatoes based on reviews from 43 critics with an average rating of 8.05/10. The website's critical consensus says, "Slow Horses loosens the reins in a more lighthearted season that doesn't quite measure up to the series' high bar, but it still excels as one of the most compulsively watchable offerings on television." On Metacritic, series five has a weighted average score of 79 out of 100 based on 17 critics. Oldman was nominated for his third Golden Globe, third Emmy Award and second Screen Actors Guild Award for his performance, whilst Lowden received a second Emmy nomination. The sixth series has received a 100% approval rating from Rotten Tomatoes based on reviews from 36 critics with an average rating of 8.45/10. On Metacritic, series six has a weighted average score of 85 out of 100 based on 12 critics.