Trains have started to run again but rail passengers have been warned to expect delays, with some trains possibly cancelled.
The person was hit by a train near Burnham. Trains have started running again, but delays of up to 30 minutes are expected between London Paddington and Reading until around 3.15pm.
First Great Western @FGW tweeted: "A person has been hit by a train at Slough meaning trains may be delayed or cancelled. Updates to follow shortly."
Commuter Graham Thomas, @thegrahamthomas , tweeted: "The train has stopped outside Slough due to a fatality. Get the impression we'll be here for some time."
Network Rail, British Transport Police and emergency services are at the scene.
Bus services were also affected because of the closure of Brunel Way, which has now reopened. First Berkshire tweeted: "Brunel Way in Slough has reopened. Routes 1B, 2 and 5 are now serving normal stops at Slough Bus Station."