The centre-half heads to The Valley after putting pen to paper on a three-year contract with the Addicks.
Although the fee has been described as undisclosed, it’s reported to be in excess of £200,000 for a player whose contract with Morecambe was set to expire at the end of the season.
Lavelle, who skippered the Shrimps to promotion via last season’s play-offs, departs after 165 appearances and six goals for the club.
The 24-year-old, who had turned down the offer of a new deal at Morecambe, had been previously linked with clubs including Blackpool, Wigan Athletic and Wycombe Wanderers.
Instead, he makes a move to the capital and becomes the second player to leave the club on deadline day following the departure of Kelvin Mellor to Carlisle United.
Shrimps’ co-chairman, Graham Howse, said: “Sam has been a great servant to Morecambe and we made him a fantastic offer to stay on a two-year contract.
“However, when it became clear that he wouldn’t sign, we had to look after the interests of the football club by listening to serious offers, knowing that we would need to plan for the rest of the 2021/22 Sky Bet League One season and beyond.
“Charlton Athletic made us an excellent offer and this transfer therefore represents excellent business for Morecambe Football Club, as we continue to invest on and off the pitch to ensure that we are competitive and sustainable in League One.”
Lavelle’s exit leaves Morecambe boss Stephen Robinson with a choice of Anthony O’Connor, Ryan Delaney, Scott Wootton and Jacob Mensah for the central defensive positions.
For his part, Robinson was philosophical about Lavelle’s decision to accept Charlton’s offer.
He added: “Sam has been excellent since I came into the club, both on and off the pitch.
“We made him a very good offer to stay, but he made it clear he wanted to pursue opportunities elsewhere, which is every player’s right.
“With just 10 months left on his contract this transfer is both a very good deal for the club and a good opportunity for Sam.
“He will be difficult to replace at this stage, but we were prepared for the possibility and have players in the building that we believe can step up and enable us to continue building on our positive start.
“We wish Sam all the best in his future career and thank him for his contribution to Morecambe FC.”
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