Emery confirmed Martinez, who missed out on a desired move to Manchester United, is available and in Villa’s squad for Saturday’s trip to Everton.
The 33-year-old was dropped for Villa’s last match, a 3-0 defeat to Crystal Palace, because Emery was concerned about his focus.
But on Friday the boss described Martinez’s commitment to Villa as “massive” and expressed his own happiness the World Cup winner remains on the books.
Emery said: “Staying here is good news, I am so, so happy. He is the best goalkeeper in the world, his commitment to Aston Villa is massive.
“He is always training to get his best, respecting Aston Villa. Some circumstances happen, everyone is happy, the energy today was very good.
“Emi is happy again and now he knows his challenge is with Aston Villa and his national team.
“I am excited and motivated and I am wishing to playing the game tomorrow against everyone in a new stadium and they are playing very well.”
Martinez's future became the subject of speculation after he left the pitch in tears following the final home match of last season.
But while the keeper was eager to seek a new challenge - and Villa open to selling - no offers to take him on a permanent deal were made, with United failing with a loan bid in July.
United rekindled their interest in the closing days of the window but ultimately decided to sign Senne Lammens from Royal Antwerp instead, meaning Martinez stayed put.
"Everything happens with players, maybe staying, maybe they were close to leaving, maybe other players were close to others or to join us," said Emery. "It's normal, I understand it completely, everything."
Emery confirmed deadline day signings Harvey Elliott, Jadon Sancho and Victor Lindelof will all be in Villa's squad at Everton.
Boubacar Kamara and Amadou Onana remain out with hamstring injuries, while Ross Barkley is absent with what the Villa boss described as a "personal issue".