MLB reinstated the 14-year veteran after he went through an appeal process.
Markakis changed his mind following his initial decision to sit out over health concerns. He made the decision after a conversation with teammate Freddie Freeman, who contracted COVID-19 and experienced symptoms such as a high fever.
"I'm going against my (previous) decision," Markakis said Wednesday, according to Gabe Burns of The Atlanta Journal-Constitution. "I'd like to come back. In the pit of my stomach, I felt like I needed to be out there."
Of the 14 major leaguers who opted out, Markakis is the first to return.
Under MLB rules, a player can come back from the restricted list if an application is submitted for reinstatement prior to Aug. 1, reports O'Brien. He adds that at the time of Markakis' decision, players who weren't considered high risk were believed to be ineligible to play for the rest of the campaign if they decided to sit out.
"It's been in my blood since four years old," the former All-Star said. "And it sucks watching baseball when you know you can still go out there and compete and play on a daily basis. And it eats away at you a little bit."