The Guard, known as a Conductor in the US, blows his whistle when it is time for trains to leave and sits in the brake van for goods trains or the brake coach for passenger trains, where he can apply the brakes in case of an emergency. Guards also have two flags, one red and one green. The green flag means "all set" and the red flag means "danger" or "stop". They often tell the driver what to do.
A North Western Railway guard's uniform consists of blue trousers, a black tie, a white shirt with a long blue overcoat, and a blue cap. Guards on the Skarloey Railway wear the same uniform in a blue-grey colour.
- Keith Wickham (UK/US; eighteenth season onwards)
- Windson Liong (UK/US; Number One Engine)
- Shinobu Satouchi (Japan; James and the Coaches and Edward the Very Useful Engine)
- Kōzō Shioya (Japan; Thomas and the Guard, Break Van and You Can't Win)
- Katsuji Mori (Japan; The Flying Kipper and Percy's Promise)
- Toshio Kobayashi (Japan; Peter Sam and the Refreshment Lady)
- Takeshi Endo (Japan; Special Funnel)
- Moriya Endo (Japan; Something in the Air)
- Yasuhiko Kawazu (Japan; Thomas, Percy and Old Slow Coach)
- Nobuaki Kanemitsu (Japan; Toad's Adventure)
- Hiroo Sasaki (Japan; Thomas and the Emergency Cable)
- Tōru Akiyoshi (Japan; The Adventure Begins)
- Andre Rinaldi (Brazil; Thomas and the Emergency Cable)
- Volker Bogdan (Germany; Audio Book 4 and 5 only)
- A miniature model of a guard is now on display at the Hara Model Railway Museum.
- James' guard that appears in the first season episode, James and the Coaches, looks like Ringo Starr.