The former Leeds United player, 23, previously captain of the Finnish under-21 side, has linked up with Finland at their training camp in his homeland ahead of two pre-tournament friendlies against Sweden (May 29) and Estonia (June 4).
Also named in the squad are Norwich City striker Temmu Pukki, Bristol Rovers keeper Anssi Jaakkola and QPR defender Nicholas Hämäläinen.
Finland face Denmark in Copenhagen in their Group B opener on June 12 and then tackle Russia in Saint Petersburg four days later.
Their final group game is against Belgium in Saint Petersburg on June 21.
Halme's elevation follows on fellow defender Michal Helik's recent call-up into the Poland squad for the finals.
Helik made his international debut in the last international break, making his bow in Hungary before starting against England in a World Cup qualifier at Wembley.
The former Cracovia centre-half has linked up with his international team-mates for a training camp in Opalenica where Poland will take on Russia and Iceland in warm-up friendlies.
They will be based in Gdansk for the finals.
Poland open up in Group E against Slovakia in Saint Petersburg on June 14 before heading to Seville to face Spain five days later before their final group game against Sweden, back in Saint Petersburg, on June 23.