Justin Holbrook is confident he can turn around the fortunes of NRL's bottom club after agreeing to join the Gold Coast Titans at the end of the season.

Holbrook, 43, transformed the fortunes of St Helens after joining them on a two-and-a-half-year contract in May 2017 but rejected their offer of a new deal in order to return to the NRL, where he was assistant coach at Sydney Roosters.

Titans announced on Wednesday that Holbrook had agreed a two-year contract to succeed fellow Australian Garth Brennan, who was sacked earlier this month with the team bottom of the table.

"It's a great challenge for me," said Holbrook at his weekly press conference. "From speaking to Mal Meninga in particular, the club have got the right people in place now.

"It will give me every chance to turn them around. I understand from an outside perspective that there's issues, but that's part of the challenge I will look forward to trying to improve."

Confirmation of the news Saints fans were dreading came just four days after Holbrook guided their team to a first Wembley appearance for 11 years and they will take on Warrington in the Challenge Cup final on August 24.

Saints are also 10 points clear at the top of Super League and have won 62 of the 78 matches under Holbrook, who said he agonised over the decision to leave.

"It was a very awkward situation because I have always been happy here and I still am," he said.

"If someone had said that in a year or two's time I could definitely go back into a job after some more success here, then you'd definitely do it.

"But there is just so much uncertainty in coaching and you have to take opportunities when they arise and that's the toughest part of it all."

St Helens chairman Eamonn McManus said: "From a St Helens perspective, we are clearly disappointed that Justin has ultimately decided not to enter into a new contract with us.

"We did everything practical to persuade him to stay, but we must respect his decision to join the Gold Coast Titans and to return to Australia with his young family."

McManus says the search for Holbrook's successor is already under way and it would be no surprise if they continue Super League's trend of picking assistant coaches from the NRL.

Titans executive chairman Dennis Watt said: "The English Super League has proven to be a successful system for the next generation of top-level coaches to finish their apprenticeships.

"The last two coaches to come back to the NRL after coaching in Super League were Michael Maguire and Trent Robinson and both won premierships on their return to Australia.

"We would love to see Justin continue that tradition."

Holbrook says he would be happy to help Saints unearth his successor and believes appointing another NRL assistant could be the right model.

"I think for me, it's been fantastic," he said. "If I'm a club in Australia, I would be thinking this is a definite pathway to explore.

"If you go from an NRL assistant's role straight into a head coaching role at the same club, you'd always be thinking it's someone else's team you're taking on.

"For me to come here and do two years as a head coach in Super League, that's a much better pathway.

"It ticks all the pathways to prepare you to coach there and being a head coach in Super League has given me confidence to take it on at Gold Coast."