Justin Holbrook says the Titans can become "a truly great club" after being on Wednesday night.
The 43-year-old St Helens mentor will join the club in the off-season after the departure of Garth Brennan.
"The ingredients for a truly great club already exist at the Titans, and I am looking forward to moving to the Gold Coast to play my part in turning that vision into a reality," Holbrook said.
"The Titans are a very strong club backed by a strong rugby league community, with a fantastic junior nursery that feeds an exceptional development and pathway system.
"I can't wait to begin working with the excellent people already within the organisation to help the club reach its true potential.
"I will of course be sad to leave St Helens, and will always be thankful for the opportunity and support that the club and its amazing fans gave to me.
"I will never forget my experience at St Helens, and hope to replicate it in my next challenge with the Gold Coast Titans."
The club delayed the official announcement of Holbrook's signing at his request so he could deliver the news personally to his players and staff at St Helens.
"I would like to make special mention and thank the Gold Coast Titans for allowing me time to address my current players personally regarding my decision to join the Gold Coast, which could only occur this morning due to our training schedule," he said.
"It was important the players heard it first from me, not by reading it online, as I have created an honest and trusted environment here at St Helens which needed to be respected."
