Police were called to the station at 10.45pm yesterday (April 9) after a casualty was reported on the tracks.
Officers and paramedics attended but the person was pronounced dead at the scene.
The incident is not being treated by the police as suspicious and a report is being prepared for the coroner.
Lines were closed for three hours between Alexandra Palace and Welwyn Garden City.
Stations were not served by any trains in this time, including New Southgate, Oakleigh Park, New Barnet, Hadley Wood, Potters Bar, Brookmans Park, Welham Green, Hatfield and Welywn Garden City.
If you feel affected by what has happened and wish to find support, you can contact the Samaritans on 116 123 via phone for a confidential chat or email jo@samaritans.org.
A Thameslink spokesperson said at the time: “It is with great sadness that we report a person has been hit by a train between Alexandra Palace and Knebworth.
“All lines are blocked between these stations whilst the emergency services work to deal with this incident.”
A British Transport Police spokesperson said: “We were called to New Southgate station at 10.45pm on Wednesday 9 April following reports of a casualty on the tracks.
“Officers attended along with paramedics but sadly a person was pronounced dead at the scene.
“The incident is not being treated as suspicious and a file will be prepared for the coroner.”
