The highly-rated full-back has established himself as a key member of Chris Powell's side since coming through the ranks at The Valley.
A number of Premier League clubs are thought to be admirers of Solly, but Charlton have moved to tie him down to a new long-term deal.
Powell was delighted to secure the defender on a long-term basis and feels he deserves his new contract
"I'm really pleased we've managed to get Chris done," Powell told the club's official website. "It's fully deserved after his exploits over the last couple of seasons since I've been here.
"It's important to get your players, especially young players that have made an impression, tied down to the club and he's an academy product that has blossomed in the side and has gone from strength to strength.
"It's always important and it's a good sign that we've been able to do it and I'm really pleased for Chris because now he can fully concentrate on his football."