The 30-year-old, once one of the most prolific scorers in the Bundesliga, was plagued by injuries and lack of form during two seasons with Fiorentina, causing him to lose his place in the national team.
He missed the 2014 World Cup and has made only four appearances since Euro 2012, all in friendlies, as his career slid downhill.
However, a move on loan from Fiorentina to Besiktas has done him the world of good and he is this season's top-scorer in the Turkish league with 19 goals.
"We have observed Mario in Turkey and he clearly has a lot more self-confidence," Loew told a news conference.
"We have seen him in training, he has won back trust in himself and that shows in his body language.
"He is always dangerous around the goal, he always worries the opposition and I plan to start with him tomorrow. He has also earned his chance in training in the last three days."
Loew said he had also had a "long talk" with Mario Goetze, scorer of the winning goal in the 2014 World Cup final against Argentina, who has made only eight Bundesliga appearances for Bayern Munich this season.
"We spoke about his general situation with Bayern Munich," said Loew, adding that Goetze would start Tuesday's friendly at home to Italy.
"He's got a bit of catching up to do physically. He needs match practice. We can help him a bit with the national team."
The world champions, who have been drawn with Poland, Northern Ireland and Ukraine in Group C at Euro 2016, are due to announce their squad on May 17, although they have several injury worries.
Captain Bastian Schweinsteiger will miss the two friendlies after partly tearing ligaments in his right knee while central defenders Jerome Boateng and Benedikt Hoewedes are also sidelined.
(Writing by Brian Homewood in Berne, editing by Ed Osmond)
