Leiter joins teammates Alex Rodriguez, Derek Jeter and Johnny Damon on Team USA. Bernie Williams is the only other Yankees player in the tournament, playing for Puerto Rico.
"I knew yesterday was the day, because everybody was leaving today," said Leiter, who will fly to Arizona after the Yankees' spring opener on Thursday afternoon. "I knew I had a chance."
Leiter had a rough season in 2005, going 7-12 with a 6.13 ERA for the Marlins and Yankees. But the southpaw had some success in a relief role late in the season, so he will likely be used as a reliever for Team USA.
"Believe me, I saw my numbers last year," Leiter said. "I'm grateful to be on the team. I know I can help."
Manager Buck Martinez informed Leiter that he would pitch behind Dontrelle Willis in Wednesday's game against Canada.
Leiter has been a proponent of the World Baseball Classic since the beginning, possibly viewing the opportunity to represent his home country as a fitting finish to his career.
Leiter plans to return to Yankees camp after the Classic, making one last attempt to catch on with the team before Opening Day. Leiter, who is in camp as a non-roster invite, doesn't believe that being away from camp for as many as 18 days will hurt his chances of making the team.
"Nothing was guaranteed; the roster was set, and even if I chose to stay, there's no guarantee of me making this team," Leiter said. "I understand that completely. Joe Torre knows what I can do, and every person in this camp knows what I can do. I'm not a young kid who is going to be a surprise. They know."
For now, Leiter's goal is to bring home the World Baseball Classic championship trophy for Team USA. Even with the tournament's latest defections, Leiter believes that the Classic will be one of the greatest baseball events ever staged.
"Is every great player participating? No," Leiter said. "But is this the best compilation of baseball players in any single tournament in the world, ever? Yes. It's better than any Olympics, talent-wise, no question about it.
"I'm going to sense and feel the pride of wearing the 'USA' on my chest," he added. "I'll wear it proudly and hopefully represent and bring home the trophy."