The London-based club did not disclose the deal's length though.
"I'm absolutely delighted to have signed a new long-term contract," Walcott told the club's official website.
"I'm so happy here and just want to say thanks to everyone who has helped me get to this point in my career.
The England ace joined Arsene Wenger's side from Southampton in the winter of 2006 on a £ 5million deal, and has been making tangible progress ever since.
After putting his signature to the improved agreement, Walcott voiced his satisfaction over the rewarding contract, and heaped praise on Wenger and his teammates.
"Together with the belief of my team-mates, the boss and everyone on the staff, everyone has got behind me here at Arsenal which is brilliant," he said.
"It's fantastic to work with the best manager in the world and play at Emirates Stadium, which is an unbelievable place to play in.
“I just want to continue playing my football at this club and look forward to many successful seasons ahead."
Wenger himself expressed his happiness to see Walcott extend his stay at the Emirates Stadium.
"We are absolutely delighted that Theo has committed his long-term future to Arsenal Football Club,” the Frenchman said.
"Theo is an intelligent player with amazing ability and speed, and has developed extremely well this season.
"At still only 20 years of age, Theo has huge potential for the forthcoming years and we are all looking forward to see him grow even more in an Arsenal shirt."