The 28-year-old made over 150 appearances across five years for Hearts, scoring eight times for the club.
The Australian international turned down the chance to stay in Edinburgh and follows manager Derek McInnes and striker Lawrence Shankland in moving from to Glasgow this summer.
Devlin has signed a deal which will take him through to summer 2028 and has the option of an additional year.
The Sydneysider has been capped five times by the Socceroos and was a part of the squad that reached the round of 32 at the World Cup, but failed to make a single appearance.
"It feels amazing. I am obviously so happy to get it over the line; with the gaffer coming here and a lot of change happening at the club, it feels like a great time to be coming here," Devlin, the sixth Rangers signing of the summer, told the official club website on Saturday.
"It is just an absolute honour and privilege; I am so aware, being in Scotland for a while now, the size of the club and everything that comes with playing at such a massive football club.
"To call myself a Rangers player now feels pretty special and I just cannot wait to get started."
On Friday evening, Devlin said it was "not a decision he took lightly" after deciding against extending his five-year stay at Tynecastle.
He was one of the key players in the Jambos' stirring title challenge that fell short on the final day at Celtic last term and, after running down his contract, was made an offer to stay that would have seen him become the highest-paid player at the club.
"Saying goodbye is never easy, especially to a club that has meant so much to me," Devlin posted on Instagram.
"This club has been so much more than just the place where I played football. It became my home, and I'm grateful for every moment.
"Playing for Hearts has been everything I dreamed of and more. European nights, derby wins, and the incredible season we've just had are memories I'll cherish forever.
"Hearts also gave me the opportunity to live out my dream of playing overseas and representing my country at two World Cups, something I'll always be thankful for.
"This wasn't an easy decision, and it certainly wasn't one I took lightly. I hope you can understand. Thank you to everyone at the club for believing in me and allowing me to be part of something so special.
"Hearts will always hold a special place in my heart. I wish everyone connected with the club nothing but success in the future."
7°C