BTP officers were called to the railway station in Portland Road, Hove, at 9.30pm last night (November 8), after receiving a report that a person had been struck by a train.
They were joined by Sussex Police and medical emergency teams who found the woman and she was declared deceased.
A BTP spokesman said: “The identity of the woman has not been confirmed but the incident is being treated as non-suspicious.
“Officers are currently working to establish the identity of the person, and inform their next of kin.
“HM Coroner has been notified and BTP are conducting an investigation in to the events surrounding this incident.
“It is requested that any information about this incident be passed to British Transport Police by contacting 0800 405040.”
All lines between Brighton and Worthing were blocked until around midnight due to the incident.