The 22-year-old centre-back joined the Magpies' Academy in 2019, spending two years on Tyneside, before departing the club in June following the expiration of his contract.
The towering defender, who has represented Guadeloupe internationally at youth level, made a total of 27 competitive appearances for United's second-string and has now signed for the Reds on a two-year deal with the option of a third year.
Crawley manager, John Yems, told Crawley's official website: "Ludwig has been around the place for a while now, he’s been training with us as well as at other clubs and scored against West Ham.
"It is great that we have been able to land Ludwig and I wish him all the best here at the club and I hope he can be a big part of our squad.”
Owen Bailey has also joined National League North outfit Gateshead on a one-year deal with the option of a second year extension.
The 22-year-old, who made his first-team debut during Newcastle's pre-season tour of China in the summer of 2019, completed a successful trial with the Heed and will link up with Mike Williamson's squad ahead of the 2021/22 season.