Wormull replaces John Maggs who stepped down last week.
Chairman Brian Suckling said: “We are delighted to have appointed Simon.
“I have watched Simon’s career develop since I first came across him as a ten-year-old during my time at Three Bridges.
“We are delighted to have him on board. He will bring great cohesion between our first team and youth set-up as well as a lot of experience.
“From the low last week of John deciding to move on, now we have an almighty high of Simon joining us. We are looking forward to getting started.”
Wormull began his playing career at Tottenham Hotspur where he played in the 1995 FA Youth Cup final and also appeared for the first team in the Intertoto Cup.
After short spells with Brentford, where he made five Football League appearances, and Brighton and Hove Albion, he played for Dover, Rushden and Diamonds – who he won the Conference with in 2001 – Stevenage, Hornchurch, Crawley Town, Lewes, Eastbourne Borough, Farnborough, Lewes again and Three Bridges. He also played seven times for the England semi-professional side.
He had a short spell as caretaker manager of home-town club Crawley Town in 2005 and was appointed Lewes manager in January 2012, stepping up from running the youth team.
Now 36, Wormull parted company with Lewes at the end of the 2012-13 season.
He said: “I’m delighted to accept the offer to become manager of Crawley Down Gatwick.
“It is exactly what I want to do in terms of building something long-term.”
Updated 07:43 - 4 Jun 2013 by Richard Munn