"I'm delighted to get everything done and dusted and now it's a chance for me to concentrate on my football," Fleck told the club website.
Fleck made his Rangers debut aged 16 and has started 11 games this season for the league leaders, scoring twice.
There had been speculation that Fleck could have left the club after he rejected new terms in January, but the youngster said he was delighted to remain at Ibrox.
Getting my future resolved allows me to focus totally on what we need to do John Fleck "Talks have been going on for a few weeks now and some things were written about me looking to move on, but I have always wanted to stay with Rangers," he said.
"It's great for me that I've got my future sorted out. I'm still only 18 and, to be getting a chance to play for a club like this, is fantastic at my age.
"I've been getting a few opportunities to play in games and come off the bench and that can only help me in the future."
Fleck said Ibrox was the best place for him to improve as a player in the long-term.
"More immediately, I'm desperate to help the team retain the league title over the next few weeks," he added.
MY SPORT: DEBATE Give your reaction to Fleck's new contract "We are in a good position in the SPL table. But, although a lot of people are saying the championship is already won, we have a bit to go yet before that's the case.
"Celtic could still come back and make things hard for us, so we are all concentrating on making sure that doesn't happen.
"Personally, getting my future resolved allows me to focus totally on what we need to do and I'm ready to play my part between now and the summer."