Bailey, 28, follows Nick Kouparitsas, signed from Sydney Roosters, in moving to London for next season after negotiating a release from the final year of his contract with the Sea Eagles.
The back-rower, who has signed a three year deal, said: “I am very excited about signing for Harlequins Rugby League and looking forward to life in London. I have spoken extensively with Acting Head Coach, Rob Powell, about this opportunity and I have been very impressed with the ethos of the club and where they want to be in terms of Super League and developing home-grown players. Hopefully, I can join the other experienced squad members and help the club achieve their goals.”
Bailey is the younger brother of Wigan back-rower Phil, who is set to join Salford for next season, and will join up with his new team-mates for pre-season training next month.
Powell added: “This is a massive signing for the club, Chris comes with a high profile and a proven track record in the NRL. He is a game breaker with fantastic ball playing and running qualities who matches this with being a really strong defender. This means he is comfortable either in a role as a back rower, on the edge, or as a stand off.
“The Super League will suit his style and he will add a lot of experience to our squad. We are looking forward to welcoming him to London.”