The 28-year-old, who was part of the Socceroos' squad for the World Cup, was one of the key players in the Jambos' stirring William Hill Premiership title challenge last term.
Hearts made Devlin an offer that would have seen him become the highest-paid player at the club following the departure of captain Lawrence Shankland to Rangers.
New boss Wouter Vrancken had planned to speak with the Australian this week after his involvement in the World Cup came to an end last Friday.Â
However, Hearts revealed on Friday that Devlin has not given them a definitive answer ahead of their stated deadline.
"Heart of Midlothian can confirm that Cammy Devlin will not be returning to the club," the club said in a statement.
"Cammy was given a deadline by the club to commit to taking up the offer of a new deal, which he has failed to meet, and therefore leaves under freedom of contract.
"Cammy joined Hearts in August 2021 and would go on to make 176 appearances in maroon, scoring eight goals. The club thanks Cammy for his time at Tynecastle Park."
Devlin, who has interest from Major League Soccer clubs in America, departs Tynecastle as Hearts' second-highest overseas appearance holder behind former captain Marius Zaliukas.
Devlin was part of the Socceroos' World Cup squad, but was an unused substitute.
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