The 42-year-old man was discovered in wetland at the Medmerry Nature Reserve, in Earnley, on Tuesday by Coastguards.
Sussex Police said the incident, which took place in the Selsey area at about 17:00 GMT, was being treated as a "tragic accident".
The Air Accidents Investigation Branch (AAIB) and British Hang Gliding Association have been informed.
A spokesman for Sussex Police said they believed the AAIB would be "leading on the investigation into the cause of the crash".

Helen Garner initially dismissed the message from Yale University as a hoax.
"I thought what the hell is this? Somebody's having me on," Ms Garner told the Australian Broadcasting Corp.
She was going to delete the email but thought to call her publisher, who informed her that the Windham-Campbell prize was in fact real.
The Windham-Campbell prize is one of world's richest literary awards, according to reports.
Garner, 73, won for her body of non-fiction work. She is also the author of novels and screenplays, including 1977's Monkey Grip, considered a classic of Australian literature.
She was not the only author to be taken aback by the surprise award, because the prizes have no submission process.
"Writers are judged anonymously and unaware that they are in the running," Yale says on its website.
A hang gliding pilot has died in an accident at a nature reserve near Chichester in West Sussex.
[NEXT_CONCEPT]
An Australian author says she "fell off her chair" when she discovered an email about a $150,000 (A$207,000; £106,000) literary award was not a hoax.