Martinez had been confident his talisman would be available for the tournament despite a facial injury suffered in Manchester City's Champions League final defeat to Chelsea.
De Bruyne sustained a fractured nose and left orbital in a collision with Antonio Rudiger, and was clearly in distress as he left the field in Porto.
However, after medical assessments and a minor surgical "intervention" – as Martinez described it – De Bruyne has been passed fit to link up with Belgium's squad on Monday.
"After looking at the images, it was decided Kevin needed a little bit of an intervention and that has taken place today, everything went really well, really positive, so we're looking forward to Kevin joining us on Monday, and he will join the squad for the Euros," Martinez told a news conference on Sunday.
Explaining the procedure, which should allow De Bruyne to play without needing to wear a mask, Martinez said: "I'm not the right person to talk in medical terms, it was just necessary for the long-term structure of the eye socket.
"It wasn't the type of surgery that is for the full structure of the front of the bone, it was just to make sure in the long-term there are no issues, but it is not a surgery as such that he needs a long time recovery, it was just to make sure the area was stronger, it took 20 minutes, went really well and the medical department are really happy.
"He's really good, he's in good spirits and can't wait to get on the pitch. This is not a surgery that stops you getting back in activities, it is the opposite, it gives you the opportunity to not need protection to play, so that's been really good news from that point of view and it's been done at the right time to see Kevin involved in the squad.
"If anything it has accelerated [his comeback] because he doesn't need protection. We believe that the area of the fracture, medically, he could even exercise without a mask, so in the medical process you need to take every day, and then when the swelling went down they were very happy.
"Because of this support in the eye socket, the structures are stronger than normal, so it's not an area that he'll need a mask, but probably in the next few days we can get the doctor to speak in more detail."
However, De Bruyne is unlikely to be available for Belgium's opening group game against Russia on June 12.
"We were always taking the timeline of him not being involved in the first game, I don't think medically that has changed, but we need to take it day by day," Martinez added.
"I can only give you clear, specific timelines when the players are training, when they are in a treatment room and in medical care, it's impossible to put that timeline. We've got another 28 players who have been working extremely well."
While De Bruyne may be out of the Russia clash, Belgium's other star playmaker, Eden Hazard, is expected to be fit, with Martinez confirming the Real Madrid forward will feature against Croatia in a friendly on Sunday.
"Eden is almost free in every area. He had a really good workout and I feel he's fit for tomorrow," Martinez said.
"It's more a case of an introduction into the game. I don't think he'll start the game, but I think he'll finish the game, and it'll be a period to make sure he's back in a game scenario. From a physical, medical point of view, he's ready.
"Eden is someone who enjoys being on the football pitch, it's second nature. The hardest moments a player has is when you're injured and cannot do what you're really good at. I see Eden with a good feeling, now it's about building that confidence in order to push himself to the limit."
