The 19-year-old, who has starred for Germany's Under-21 side, was included in the preliminary senior squad by head coach Joachim Löw for next month's tournament in Austria and Switzerland from June 7 to 29.
Marin has helped his side win promotion back to the Bundesliga this season after a year in the second division and the teenager admitted he was stunned.
"I am totally overjoyed and can hardly believe it," said Marin, who flies out with the squad on Monday to their Spanish training camp. "It was hard to take it all in at once. I am really looking forward to the 12 days in Majorca now."
And there was also a surprise call-up for Bayer Leverkusen goalkeeper Rene Adler at the expense of Germany's reserve 'keeper Valencia's Timo Hildebrand, while Hanover 96's Robert Enke has also been chosen.
"I am surprised, shocked and also irritated," said Hildebrand, who heard the announcement by television having struggled to break into the Valencia team this year. "Clearly there is nothing else for me now, when you hear of a decision in this manner. Of course, I have to accept it, but I don't understand it."
Striker Patrick Helmes has also made the squad after his second-division side Cologne won promotion back into to the Bundesliga.
Löw will take his squad to Spain on Monday for a training camp and will cut his squad to 23 when the Euro 2008 squad is finalised on May 28.
"Now the serious work begins for us of choosing a team for the European championships," said Löw. "We want to exhaust all possibilities in the enlarged squad and we have the luxury of a training camp to scrutinise players. This is both our right and obligation. We need to see how players cope under pressure."
With six strikers in the extended choice, there is plenty of competition and the pressure is on Helmes and Oliver Neuville from Borussia Mönchengladbach to prove themselves having been plucked from Germany's second division.
Germany are in Group B and play Poland on June 8, Croatia on June 12 and co-hosts Austria on June 16.
Goalkeepers: Jens Lehmann (Arsenal/ENG), Robert Enke (Hanover 96), Rene Adler (Bayer Leverkusen)
Defenders: Christoph Metzelder (Real Madrid/ESP), Per Mertesacker (Werder Bremen), Philipp Lahm (Bayern Munich), Arne Friedrich (Hertha Berlin), Marcell Jansen (Bayern Munich), Clemens Fritz (Werder Bremen), Heiko Westermann (Schalke 04)
Midfield: Michael Ballack (Chelsea/ENG), Thomas Hitzlsperger (VfB Stuttgart), Simon Rolfes (Bayer Leverkusen), Torsten Frings (Werder Bremen), Bastian Schweinsteiger (Bayern Munich), Piotr Trochowski (Hamburg), Tim Borowski (Werder Bremen), Jermaine Jones (Schalke 04), David Odonkor (Real Betis/ESP), Marko Marin (Borussia Mönchengladbach)
Forwards: Miroslav Klose (Bayern Munich), Lukas Podolski (Bayern Munich), Mario Gomez (VfB Stuttgart), Kevin Kuranyi (Schalke 04), Patrick Helmes (Cologne), Oliver Neuville (Borussia Mönchengladbach)