The 21-year-old, who has worked this way through the ranks at Sixways having initially started in the club's thriving mini/junior section, was a part of the England Under 20 team that achieved the Grand Slam in the Six Nations of 2008.
Worcester born and bred Arr, who has become a regular starter this season and has played a total of 43 times for Warriors and scored two tries, will now remain at Sixways Stadium until at least 2012.
He becomes the latest home-grown product to commit to Warriors in recent months with Matt Mullan, Miles Benjamin, Chris Pennell and Greg King all agreeing new deals.
"It is great news that Jonny Arr has decided to extend his stay at the Warriors," said Director of Rugby, Mike Ruddock.
"He is a fine young player and fine young man who is developing very nicely at Sixways Stadium.
"Jonny has really produced during the second half of this season and has capitalised on Ryan Powell's injury to make 22 appearances already. The opportunity has allowed him to maintain a run of games as the No.1 scrum half at the club.
"During that time he has displayed his all-round ability, his maturity and composure under pressure and his ability to bounce back if things don't go to plan.
"He is a great young prospect and I expect to see him developing further during the next two years, hopefully to the point where one day he might follow the likes of Miles Benjamin and Tom Wood into the England Saxons squad or even Matt Mullan into the full national squad."