The 25-year-old, who joined the Canaries in January 2012, is the only Norwich outfield player to have featured in every Premier League match.
Boss Chris Hughton admits he is delighted with the midfielder's development as the Canaries have slowly started to climb the table.
"A new contract comes in line with Jonny's form this season, which has seen him be a mainstay of the team and put in some impressive performances," Hughton told the club's website.
"In the period of time that Jonny's been here, there's been progression in his influence in the team and in the matches, and we're delighted to be able to secure his services for the next four-and-a-half years."
Howson joins team-mates John Ruddy, the England goalkeeper, and club captain Sebastien Bassong in penning contract extensions to commit their long-term futures to the Norfolk club.
The former Leeds trainee hopes to build on his promising start to the 2013/2014 campaign. He said: "As soon as I found out there was an offer there, I was very interested in getting it signed. I am very settled here and happy to sign.
"I have really enjoyed the season so far and have had a good run in the side. I just want that to continue, and obviously staying here longer gives me the chance to do that."