The Australian midfielder completed his switch to Tynecastle Park from Newcastle Jets on Tuesday, signing a three-year deal.
Devlin was at Tannadice on Saturday to watch his new team win 2-0 to keep up their unbeaten start to the league campaign.
The deal has been in the pipeline for a number of weeks. The player had to quarantine after being involved with Australia at the Olympics in Tokyo, while there was a visa process and other necessary paperwork to be completed before he could finally join.
"Dreams really do come true," the 23-year-old said on Instagram.
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"Buzzing to be joining such a massive club, can’t wait to get started."
"It’s the perfect way to get started," he told HeartsTV. “We’ve got the international break so it’s the perfect way to gel with the boys, get to meet them all. They’ve been class with the way they have welcomed me in. It’s such a good group to join and we're at the top of the table so everyone is on a high.
"It’s great for me to come in and I need to work as hard as I can to get on the field. If I’m lucky enough to do that on the 12th of September I’ll be over the moon.
"A packed Tynecastle sounds like it's going to be insane. I cannot wait.”
Devlin, who took advice from Hearts legend and fellow Aussie Ryan McGowan ahead of his move to Gorgie, will add to Robbie Neilson’s midfield options.
"I love to get on the ball. I love to start build-ups, give the ball to attackers. I like to keep possession.
"In defence I like to think I run around and cause carnage and try and win back as many balls as I can to give the attackers the best opportunity to go forward.
“I like to talk a lot on the field and most importantly help the boys get three boys.”