The wildman rock star vowed to go ahead with the gig at Dublin's Lansdowne Road - despite the high profile break-up.
The concert in front of 40,000 fans will be the first time the brothers have performed together since guitarist Noel walked out of the tour after falling out with Liam over his heavy drinking.
But while the brothers have managed to patch things up, both Liam, 27, and Patsy, 32, have confirmed their marriage is over.
Definitely, not maybe
The couple are said to be talking to divorce lawyers and Gallagher was reported as saying: "It's finished, over, gone. That's it.
"Maybe I was too young but I don't think I'll be marrying again. I'm just trying to get on with my music and be a good dad. We're still talking on the phone though," he told The Sun newspaper.
An announcement on Friday night from Kensit's spokesman confirmed the three-year-old marriage was beyond being saved - ending weeks of speculation.
Oasis, who flew into the Irish capital on Friday, did their best to avoid media attention by booking themselves into four different hotels.
Fans from across Ireland are expected to watch what many predict may be the group's last overseas show.
Several thousand British followers have also made the trip across the Irish Sea.
The gig comes a week after Oasis pulled out of the Roskilde Festival in Denmark after eight fans were trampled to death as American rockers Pearl Jam played.
Kensit 'relieved'
Kensit and Gallagher's volatile relationship had seen numerous bust-ups, but was thought to be on a more even keel after the birth of their son, Lennon.
However, the strains became apparent again recently when their home was put on the market while Kensit was filming her movie Things Behind The Sun in the United States.
The actress - who was previously married to Big Audio Dynamite's Dan Donovan and then Simple Minds' frontman, Jim Kerr - was also spotted out without her wedding ring.
Asked if she was disappointed at the split, Kensit said: "It's over - no, I'm actually relieved.
"It's been over for quite a long time really," she said on ITV's London Tonight programme.
Kensit denied she had been through a rough time and said she still regarded Liam as a friend, and wished him well.