The Guards, known as Conductors in the US, are in charge of the passenger and goods trains that run on the railway, and are responsible for keeping them on time. They blow their whistle when it is time for trains to leave and sit in the brake vans for goods trains or the brake coach for passenger trains, where they 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 drivers what to do, and take tickets on passenger trains.
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.
- A miniature model of a guard is now on display at the Hara Model Railway Museum.
- James' guard that appears in the first series episode, James and the Coaches, looks like Ringo Starr.