The skipper has signed a four-year deal with Cronulla worth around $2 million.

Off-contract at the end of this year, McInnes will play out the 2021 season before he moves to the club's fierce rivals.

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St George Illawarra have expressed their disappointment at the captain's departure, the team unwilling to commit to a new contract prior to the start of the new season.

"We were well aware throughout our discussions with Cameron and his management that he wanted his future sorted prior to the season commencement," Dragons general manager of football Ben Haran said.

"There's always a process to contractual negotiations, but with our club going through a significant transition it's fair to say that Cameron and the club were working on different timeframes.

"We understood why he wanted his future sorted immediately, which has since led to Cameron and his family securing an opportunity elsewhere.

"Cameron is a quality player and person who has brought a lot to St George Illawarra since arriving in 2017, and we're looking forward to him again playing a huge role in his final season at the club."

Cronulla coach John Morris said the Dragons captain will help lead the Sharks both on and off the field.

"Cameron ticks all the boxes for us in that he has great attitude, he competes on every play and is an excellent defender," Morris said in a statement.

"Not only is he respected for what he can do on the field, he is of outstanding character, is a thorough professional who looks after himself and we are adding someone to our squad who is a leader and will be a major asset to our young developing players."

With emerging hooker Blayke Brailey under contract at the Sharks, Cronulla confirmed McInnes has been recruited to play lock.

He earned a call up in the NSW Blues squad last season on the back of his versatility, having spent much of last season at lock after Ben Hunt's shift to dummy half.

McInnes has spent the summer training at hooker for the Dragons.

"He can play lock equally as well as he can play dummy half and that versatility, especially in the modern game, is very attractive to our club," Morris said.

"Cameron has been brought mainly to play lock and will complement Blayke Brailey at hooker in a potent 9 and 13 combination that should have all Sharks fans very excited.

"He's a winner and we are very pleased he has agreed to join us in 2022."

The captain's departure comes after Tyson Frizell left for Newcastle at the end of last season. The team has also lost Gareth Widdop and James Graham in the past two years, the pair opting to return t England.

The heart and soul of the Dragons in recent years, McInnes has led the side through a turbulent period both on and off the field.

With the team underperforming, coach Paul McGregor departed midway through last season, while the Jack de Belin court case continues to cast a shadow over the club.

McInnes' future has been the subject of speculation in recent months, the hooker meeting with Wests Tigers coach Michael Maguire in December. The Bulldogs also reportedly showed an interest in signing the South Junior.

The Dragons have recently been linked to Broncos hooker Andrew McCullough, the 31-year-old having played under new coach Anthony Griffin during their time together in Brisbane.

The dummy half was also a teammate to Ben Hunt prior to the halfback's move to Wollongong.