Officers were called to the line close to Wembley Central station at 06.48 am on the 4th December 2020 following reports of a casualty on the tracks.
Paramedics also attended however sadly a man was pronounced dead at the scene.
Officers are currently working to identify the man and establish the full circumstances behind his death.
Detective Chief Inspector Paul Langley said: “We are still at a very early stage of our investigation, and are keeping an open mind as to the circumstances behind this man’s sad death.
“At this stage we believe the man reached the tracks from a nearby footbridge.
“I’d like to appeal to anyone who may have seen the man on the footbridge or in the nearby area in the early hours of this morning to get in touch with us as soon as possible.
“He is described as being between 30 and 40 years old, with dark hair and a beard, and he was wearing grey tracksuit bottoms and blacked hooded top.
“Anyone with information can contact us by texting 61016 or calling 0800 40 50 40 quoting reference 48 of 04/12/20.”