A man was pronounced dead at the scene by medics shortly after 6am after being hit by the Havant to London Victoria service.
British Transport Police were called to East Worthing station after a report that a person had been struck by a train.
Officers from Sussex Police also attended.
A file has been prepared for the coroner.
The incident is not being treated as suspicious and the line was handed back to Network Rail at 7.33am.
A statement on National Rail’s website reads: “The line has now reopened, but because of this, there are residual delays of up to 60 minutes between Brighton and Worthing. These delays will continue until further notice.”