Kelechi Iheanacho's close-range finish after 55 minutes was enough to secure the Foxes a return to Wembley on May 15th, where they will face Chelsea as they look to win the cup for the first time in their history.
The man behind the success, Brendan Rodgers, has been an influential figure in turning what was only a dream for most Leicester supporters into a truly possible reality.
The Northern Irishman spoke to the media after the game to provide his thoughts on another memorable day for the East Midlanders.
On an important victory
"It's amazing." said Rodgers.
"The club have been waiting a long time to get to the final. I thought we deserved it. We defended strongly and didn't concede any efforts on goal.
"As the game wore on we looked really bright in our attacking play and maybe should have had more than one goal. (I'm) just really pleased for everyone, the players first and foremost."
For large spells of the game Leicester were the dominant side, restricting the Saints to nothing more than half-chances.
Despite the slow start to the game, it was the designated home side that looked the most threatening, controlling the tempo of the game with their possession-based philosophy and looking to test the resolve of the Southampton defence.
Prior to the game, Ralph Hasenhuttl's side were yet to concede a goal in the cup, however Iheanacho's strike proved to be a fatal one as it secured Leicester's passage to the final.
On leading his side out at an FA Cup Final
"It will be a privilege to lead the team out to a final. I felt we deserved it, it was always going to be a tight game. We want to win it though. That’s the message. It’s brilliant for the club and I respect the wish to get there but we’re very hungry to win it."
"When we arrived here, that was the ambition. We said we wanted to be competitive. From a football perspective we wanted to be able to compete and we have been able to do that. Now we have a trophy to genuinely go for. When you fail it is an integral part of being successful. We missed out last year, so a great credit to the players this time."
When Rodgers first arrived to the club, the word on everyone's mouth was the desire to win the FA Cup.
It's been the one trophy that has eluded the Foxes domestically with no other side reaching the final more times (four) than Leicester and not win the competition.
The progress has been their for all to see and under the guidance of the 48-year-old, they are now closer than ever to adding the world's oldest cup competition to their trophy cabinet.
On Kelechi Iheanacho
"His confidence levels are very high. I thought the front two worked their socks off. They were a real threat. If he makes a mistake, he gets on with it. Whether he's inside or outside the box, he looks like he's going to score in every game."
The return to form of the Nigerian has been one of the stories of the season at Leicester and with Iheanacho scoring the winner on Sunday, it seemed a fitting tribute to his hard work.
It was only back in December that people questioned the 24-year-old's long-term future at the club after a missed penalty at Crystal Palace, however since then he has rediscovered his form, scoring his 10th goal in his last seven games.
Furthermore, his effort now makes him the Foxes leading scorer with 15 goals in all competitions and is the first Nigerian to reach that total since Odion Ighalo did back in the 2016/17 season.
On the return of fans
"It felt really good to have supporters in. We could hear a number for Leicester in the crowd. It’s a step towards getting that connection back because the game is nothing without the supporters. Hopefully at the final there can be a few more in."
Sunday's game was a momentous occasion not just on the pitch but off the pitch too as Wembley welcomed 4,000 fans back into the stadium.
The semi-final was used as one of the government's pilot test event schemes as part of the roadmap out of the Covid-19 pandemic and the crowd was the largest of any sporting event in the UK in 13 months.
It is reported that up to 22,500 fans will be allowed to attend the final but for players and supporters alike, it was welcome to see a small return to normality.
On the Chairman
"I’ve just spoken to Top there and he was over the moon. He looked very happy. It’s the early hours there, and he’s been up all night.
“I'm so pleased for him. He’s an incredible guy who has suffered these past few years. To give him that joy in being able to get to the final, and I’m very happy to do that for him."
The work Leicester have done to reach the final has been years in the making and is largely down to the chairman of the club, Aiyawatt Srivaddhanaprabha.
In normal circumstances, the owner of the Foxes, known as 'Top' would have been there to celebrate in person, however with travel restricted, his celebrations were in full swing in Thailand.
Along with the efforts of his late father, they always had a vision of transforming Leicester into a side that would compete at the top of level of English football.
In their time in charge they have guided Leicester to a famous Premier League title and now are on the verge of adding the FA Cup to their ranks, further cementing their ideology and vision.