The iconic fly-half is set for his final Six Nations tournament - he will retire from Test rugby after this year's World Cup - and had been a doubt due to taking a heavy knock to his cheekbone in early January.
However, he said at the Six Nations launch in London he would be leading world-ranked number one side Ireland onto the pitch in Cardiff on Saturday week.
"I am good to go," he said.
"I was training last week, I just had a funny face mask on and will keep that on this week and it comes off next week.
"Being injured so close to the off obviously it is at the forefront of your mind that you might miss the first game.
"The surgeon said to me, if there was a bone to damage on one's face then it was that one. That was nice to know!" he added laughing.
Ireland's conundrum throughout Sexton's time as number one has always been who is his natural successor.
Joey Carbery (27) had been seen as the heir apparent but the New Zealand-born Munster playmaker was surprisingly omitted from the squad by head coach Andy Farrell (47) last Thursday.
He called up Sexton's Leinster teammate Ross Byrne (27) and Carbery's young Munster colleague Jack Crowley (23).
Crowley started Ireland's last Test, due to Sexton suffering an injury in the warm-up, with Byrne coming on and sealing the 13-10 win over Australia with a penalty three minutes from time.
Farrell said he could understand that his call on Carbery had come as a great surprise to many.
"I understand the surprise," said Farrell.
"He (Carbery) has not been playing poorly and played pretty well from what I hear yesterday.
"Just as with other players who failed to make the squad we have had feedback.
"It was similar sort of feedback that saw Ross Byrne be out of the international scene for a couple of years till last November.
"Now he gets his chance to convert his province form to the international stage.
"Joey will be working hard to get back in but we have taken the option of the potential to go forward with Jack Crowley."
Farrell - who will hope a strong Six Nations showing leads to Ireland finally reaching at the very least a World Cup semi-final later this year - said Sexton was clearly number one but it was good to have such a scrap going on to be his number two.
"Johnny is top of the tree but he would be the first to say he has things to work on," said Farrell.
"There is a good bit of depth and people fighting and wanting to be part of this Irish squad."
