The concert at the Principality Stadium in the Welsh capital will be the first of a 41-date run of gigs spanning the world, including in the United States, Japan, Australia and Brazil.
Once-warring brothers Liam and Noel Gallagher, their bandmates and UK support acts will play in Cardiff on Friday and Saturday before five hometown gigs in Manchester starting on July 11.
Further sold-out British and Irish concerts will follow at London's Wembley Stadium, Edinburgh's Murrayfield Stadium and Dublin's Croke Park, before the international leg of their Oasis Live '25 tour.
"All that matters is how the people in that stadium feel," Liam Gallagher, 52, said on social media last week, as months of anticipation reach a climax.
Fans have been sharing their excitement at the first chance to see Oasis play live since 2009 -- or ever -- after it was long seen as a remote prospect following one of music's most acrimonious break-ups.
The band's 1990s gigs are the stuff of legend.
"The feeling is biblical!" fuel tanker driver Sean Campbell, 35, told AFP before attending Friday's gig.
"I've been waiting years for their return. I missed out on going years ago, so this is my first time seeing them live."
Ticket controversy
Oasis, famous for 1990s hits like "Live Forever" and "Wonderwall", announced its comeback tour last August, days before the 30th anniversary of their debut album, "Definitely Maybe".
The Manchester rockers split in 2009, with Noel saying he "simply could not go on working with Liam a day longer".
The Gallagher brothers had maintained a war of words about each other for more than a decade, performing individually over those years but never together.
The surprise announcement that they had finally put aside their feud to reunite sparked an online frenzy for tickets but outrage over sudden price hikes that saw Britain's competition watchdog threaten legal action.
Resale tickets costing thousands of pounds have surfaced, while fans have also been targeted by online scams.
Britain's Lloyds Bank estimated in April that victims had collectively lost more than £2 million ($2.7 million).
The tour is expected to be a boon for the struggling UK economy.
Fans could spend more than £1 billion combined on tickets and outgoings such as transportation and accommodation, Barclays bank estimated in May.
'Rough and ready'
Oasis will be supported in the UK by Richard Ashcroft, frontman of British rock band The Verve, as well as the Liverpool-formed band Cast.
The band has not released the setlist for their opening and other shows, with rampant speculation online over which classic tracks will feature and whether any new material will be performed.
There are also many rumours over the potential for special guests appearances.
Illuminated drones displayed Oasis's classic logo above the Cardiff stadium late Wednesday, in a one-night display adding to the buzz around the tour's kick-off.
Gates open Friday at 5:00 pm (1600 GMT), with the band due on stage just over three hours later after both support acts have played.
The performance will wrap up by 10:30 pm, organisers said.
The stadium, which has a capacity of 74,500 for concerts, is set to have its retractable roof closed for both nights, with an incredible atmosphere expected.
Oasis reportedly began jamming together months ago, before starting rehearsals in London more recently.
The band has reportedly welcomed several new members for the tour, including a keyboard player and drummer.
Writing in the tour programme, Noel, 58, reflected on the band's enduring popularity, saying "a new generation recognises how Oasis wasn't manufactured".
"It was chaotic, and flawed, and not technically brilliant. We were rough and ready guys from a rehearsal room, and people recognised it."
