On this day, (8 July) 26 years ago, an initial loan deal was made permanent. It's a story which began with O'Neill inheriting a tense situation at Filbert Street, four days before Christmas in 1995, after Mark McGhee's departure to join First Division rivals Wolverhampton Wanderers.
Leicester's future hinged on several key events. Firstly, the Club's decision to hire O'Neill - and not former Everton manager Mike Walker - but also the new man's decisions in the transfer market.
Izzet's arrival on loan led to his debut for the Club on 30 March and would become a defining moment, alongside the acquisitions of Steve Claridge, Neil Lennon and Julian Watts over the winter months.
The first eight games of O'Neill's tenure were winless, as Leicester drifted away from play-off contention, ahead of a trip to Molinuex to tackle City's former manager at Wolves.
A goal from Iwan Roberts and youngster Emile Heskey's brace, though, secured a 3-2 success, energising the Club's bid for a return to the Premier League.
It was still a tight affair on the final day as O'Neill's men headed to Watford. They needed a win and the man to deliver it was Izzet, netting a rare headed goal at Vicarage Road - his first for Leicester.
The London-born central midfielder instantly became a popular figure on the terraces, while another winter signing, Claridge, booked promotion in the final seconds of the play-off showpiece against Crystal Palace.
Izzet's services were secured on a full-time basis the following summer for a reported fee in the region of £800,000 and neither Leicester nor Izzet looked back as they took the top flight by storm.
Alongside Lennon and eventually Robbie Savage too, Izzet was the jewell in Leicester's midfield, a sprinkle of stardust alongside his more industrious, defensively-minded colleagues in the middle of the park.
As City lifted the League Cup, with a replay victory over Middlesbrough at Hillsborough, and finished ninth in the Premier League, there were growing calls for Izzet to receive an England call-up.
Neither Glenn Hoddle or Kevin Keegan picked up the phone, much to the increasing bemusement of the Blue Army, and Izzet, whose father was a Turkish Cypriot, later elected to represent Turkey internationally.
Whether it was his diving header in a 4-0 triumph at Derby County, a thunderous volley against Tottenham Hotspur at Filbert Street, or a ridiculous bicycle kick at Grimsby Town, the former Chelsea youth product was earning cult status in Leicester.
He was there again, exhibiting his undoubted ability beneath the iconic Twin Towers of the old Wembley Stadium, as O'Neill's men lifted a second League Cup in four seasons in February 2000.
When O'Neill departed for Celtic in 2000, Izzet remained. When Savage moved to Birmingham City in 2002, as the Club was relegated, Izzet stayed put once again, despite intense transfer speculation.
He also scored the goal which, alongside an earlier effort from Jordan Stewart, booked their promotion back to the Premier League at the first attempt with a 2-0 victory over Brighton & Hove Albion in April 2003.
By this time, Izzet had also represented Turkey at the 2002 FIFA World Cup, starring in the semi-final against Brazil, as his father's home country secured a third-placed finish in South Korea and Japan.
There was little he had not achieved at the Club. Two promotions, four top-10 finishes, two League Cup triumphs, starring in European football and enough memories to last a lifetime. But, in 2004, Leicester were relegated yet again.
Despite withstanding financial pressure to keep hold of their prized asset two years earlier, as the Club faced administration, neither Izzet nor Leicester City could realistically hope to stay together.
Now in his 30s, Izzet had one last shot to remain a Premier League player, but in truth there was very little chance City would have been able to afford to keep a player of his calibre in the second tier.
At the end of his Leicester contract, City's No.6 left for pastures new, with the best wishes of everyone on Filbert Way, linking up with Savage and Heskey across the M6 at Birmingham City.
Nevertheless, Izzet's time at the Club coincided with a golden era to be a Leicester fan. It was a time defined by players like Izzet, who has since made the city of Leicester a home for his family.
"I owe all of it, a lot of it, to Leicester and Martin for giving me that opportunity and that springboard to be able to go on and play internationally," he said recently.
"We were a bunch of lads that was put together by Martin and we literally just did our best. That’s all we could do.
"We were given an opportunity to play in the Premier League and we all really wanted to do it and we wanted to play hard for each other.
"We didn’t want to let ourselves down, we didn’t want to let Martin down, we didn’t want to let the fans down. So, personally, I’m glad that I got the opportunity to play for Leicester.
"My three kids were born in Leicester, I still live in Leicester. If you’d have said to me 30 years ago that would be the case, I don’t think I would’ve believed it.
"I thought I’d be in London doing whatever it was I’d have been doing, but Leicester’s a big part of my life. I’ve got a business here in Leicester now and everything else, so I have to thank them."
For the majority of Foxes fans of all ages who were fortunate to enjoy watching Izzet outwit the best defenders in English football, the feeling is mutual.