The Argentinian fly-half had been due to be out of contract at the end of the current campaign - however he has now committed to the Chiefs for the next two seasons.
The only hurdle to clear for Mieres was the possibility of disruptions should he be called up by the Pumas for the inaugural Rugby Championship.
However the 24-year-old, who had spells in France with Perpignan and Stade Francais, had no hesitation in putting pen to paper on a new deal.
"I'm really happy to have signed because I always said I wanted to stay at Exeter," explained Mieres.
"I knew it was a difficult contract because of the situation with Argentina, but after lots of talks both parties are happy with the contract.
"Right now it's an extraordinary situation because no one has ever experienced the competition and it's the first year.
"As I said, I wanted to stay here and Rob wanted to keep me here, so I'm really happy the club - who have been great throughout - have decided to keep me and not oppose any call-up I may get from Argentina."
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