Speaking ahead of the 70th anniversary of the failed plot, Merkel said those responsible had acted "in accordance with their conscience".
"It showed how men in an extremely difficult situation were able to take a decision in accordance with their conscience, to not be guided by unconditional loyalty but form their own idea of what was necessary for Germany," she said during her weekly podcast.
The "20 July plot", as it came to be known, saw German army officers from Hitler's inner circle team up with members of the resistance to try to blow up the Nazi leader at his headquarters in Rastenburg, Eastern Prussia, now part of Poland.
The Wehrmacht officers aimed to seize political control of Germany and make peace with the Allied forces. They codenamed their mission "Operation Valkyrie".
An aristocrat named Colonel Claus von Stauffenberg placed a briefcase containing a bomb under a table at which Hitler was seated.
The bomb killed three officers and the stenographer but the Fuhrer escaped with only light injuries.
Von Stauffenberg and several others were executed shortly afterwards, and the war continued for nearly a year.
Merkel is due to inaugurate a new permanent exhibition devoted to the assassination attempt at the German Resistance Memorial on Tuesday.
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