A 21-year-old German, escorted by his lawyer, presented himself at the prosecutor's office in Berlin on Monday and confessed to taking part in the heist, Sjors Kamstra, a spokesman for prosecutors, told a news conference.
The man had "an immigrant background" and "after intensive questioning, named his accomplices," he said.
He had also offered to return his share of the €242,000-booty, police said, although the money was currently stashed "with a third party."
The other gang members were a 19-year-old German, a 20-year-old from Turkey and another 20-year-old of unknown nationality, Kamstra said, presenting photos of the three fugitives.
Later Wednesday a second suspect, aged 20, was arrested "without resistance" after presenting himself to routine security officers in a metro station in the city, police said, without giving his nationality.
"In my opinion, the robbery on the poker championship in the Hyatt can be considered largely solved," Kamstra said.
In a spectacular daylight robbery likened by some media to the Hollywood blockbuster "Ocean's 11," the masked gang of four burst into the hotel near Berlin's Potsdamer Platz wielding machetes and handguns.
In chaotic scenes captured on television, they snatched bags of cash and struggled with security guards, one of whom managed to recover a bag, and sped away in a black Mercedes-Benz.
The tournament, the German leg of the European Poker Tour, attracted around 950 participants including German tennis legend Boris Becker with €4.7 million in prize money up for grabs.
The game continued after the raid, and the top prize of €1 million eventually went to American online poker star Kevin "ImaLuckSac" MacPhee.