The last-placed Titans confirmed on Monday that Hasler would coach the final two games of the year before stepping down, concluding a disastrous two seasons in charge of the success-starved club.
Dual premiership-winner Hasler, 64, leaves with a year to run on his Titans contract and is no guarantee to coach in the NRL again after this year.
Highly-rated Hannay will leave his post as assistant to Cronulla coach Craig Fitzgibbon, having signed a three-year deal to become a full-time NRL coach for the first time.
The 45-year-old has built an impressive resume that includes four years as Billy Slater's right-hand man at the Queensland State of Origin team.
He also led the Sharks to within an inch of the NRL finals as interim coach in 2021, and was interim coach of North Queensland in 2020 before Todd Payten's arrival.
"He's a genuine player development coach," said Titans chief executive Steve Mitchell said of Hannay.
"He has a genuine desire to come here to the coast and one of his primary drivers is to actually be the first to deliver success to the Gold Coast.
"That's a promise that we talk about a lot, but that is essential to his decision."
Hannay will have a big task to inspire sustained success at Gold Coast, who have not won a finals game since 2010 and have made the top eight only twice since then.
His appointment comes alongside widespread changes to the Titans' front office, with NRL legend Scott Sattler returning as director of football.
As general manager of football, Sattler helped piece together the club's inaugural roster, which made a preliminary final in 2010 - the club's best result to date.
He will relinquish his media duties with radio station SEN at the end of the season to take on the role.
Titans foundation player Anthony Laffranchi, meanwhile, transitions out of his role as general manager of football to become recruitment manager.
The reconfiguration comes barely two years after the club fired Justin Holbrook midway through the 2023 season to clear the way for Hasler.
That appointment appeared to signal a new dawn on the Gold Coast, with Hasler the first premiership-winning mentor to take charge of the club since its inception in 2007.
But the Titans have won only 13 of Hasler's 46 games in charge for a win rate of 28 per cent, and look likely to earn their coach's first NRL wooden spoon.
Mitchell defended the call to appoint Hasler, who has had a winning record in only one of his past five seasons as a coach.
"When we appointed Des at the time, arguably the industry said it was one of the best appointments they've seen in the game at the time," he said.
"Unfortunately, the results haven't run the way we wanted nor have they touched on our aspirations but everyone's a genius in hindsight.
"Des has done everything … to actually deliver success. You can't criticise the amount of work that's been put in."
This year Hasler became the sixth coach to reach 500 NRL games, and as recently as June the club released a media statement publicly backing him to remain coach in 2026.
But the situation appeared untenable, with the Titans finishing 11 of the past 13 rounds on the bottom of the ladder.
"This club, this community, deserves a successful NRL team and we could see that we needed to make changes to make that happen," said chairman Dennis Watt.
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