Defender Winston Reid has signed a new long-term contract with West Ham which commits him until the summer of 2021.
Blackburn have signed defender Doneil Henry on a month's loan from West Ham.
The 21-year-old, who joined the Addicks from Bury Town in 2011, made his debut as a substitute in the final game of last season.
"Good, young British goalkeepers are few and far between," Charlton boss Chris Powell told the club's official website.
"We feel we've got one who will develop into a very good goalkeeper, who will have a good career in the game.
"It's pleasing that he's agreed to sign the new contract and that he sees his immediate future here.
"Goalkeepers mature late in their careers but he's already showing signs that we've got a real talent on our hands.
"It's pleasing that for the next three years he sees his future with us."
Pope, who has had loan spells with Welling and Cambridge United since moving to The Valley, added: "It's a big club so to have a long-term future secure, for me, as a player developing, it's something you look for.
"It's about just concentrating on my work now and continuing my progression."