The 23-year-old Frenchman penned a four-year contract at Turf Moor after spending last season on loan with Levante in La Liga.
Raghouber began his development at Torcy before joining Lille’s academy at 14. He progressed through the club’s youth ranks and signed his first professional contract in 2021.
"I'm really happy to be here! It's an amazing club, with huge history and it's an exciting time to join,” said Raghouber.
"Once I heard of the interest in coming here, I knew I wanted to get the move done. I'm now ready for the next chapter in my career and to give my all for this club and the fans."
After making more than 40 appearances for Lille B, he gained senior experience with Le Mans and Dunkerque before moving to Levante.
The midfielder now arrives in Lancashire with over 100 senior appearances under his belt, adding valuable experience and depth to Burnley’s squad as he begins a new chapter with the Clarets.