Krul has agreed a five-and-a-half year deal to stay at St James' Park, while Coloccini has accepted a new four-and-a-half year contract.
The duo have been instrumental figures in the Magpies' excellent season to date and have attracted interest from rival Premier League clubs.
Dutch keeper Krul's string of impressive performances this term had seen the 23-year-old mooted as a summer transfer target for Tottenham Hotspur.
However, Krul has put to bed any speculation concerning his future by signing an extension after firmly establishing himself as Alan Pardew's first choice between the posts.
Krul, who took in loan spells at Falkirk and Carlisle United during his early days at Newcastle, has made 64 appearances for the club in all competitions.
Magpies skipper Coloccini, meanwhile, has made over 140 appearances since moving from Deportivo La Coruna in 2008 and has been an influential performer since the club's return to the Premier League.
Coloccini was due to be out of contract at the end of next season and had been linked with the likes of Liverpool in the January transfer window.
Newcastle had been trying to agree an extension with the Argentina international for several months and have now finalised a deal with the 30-year-old.