The Saints take on Hearts in tomorrow's Hampden showdown, 26 years since the club last won a major trophy.
The Black and White Army celebrated long into the night when their side scooped the 1987 Scottish Cup by defeating Dundee United 1-0.
They came close to winning the League Cup in 2010 when they met Rangers in the final, but lost when Kenny Miller scored six minutes before time.
But Paisley Buddies and local businesses in the Renfrewshire town are optimistic ahead of tomorrow's match, when the club will have their chance to clinch silverware once again.
Allan Boyd, 42, a postman from Paisley, said: " I'm nervous as hell to be honest. The atmosphere is definitely there, but we want to go one better and come home with the cup.
"I've been a fan for 42 years so I'd burst out crying if we won, I won't lie about it.
"It means that much to me."
All shops on the High Street agreed to have the area closed off on Sunday to make way for the celebrations, which are expected to last well into the evening should the Saints win the trophy.
The council have extended the licence for some of the local pubs, and extra police will be on the scene to manage the hundreds of people expected to gather in the town centre.
Festivities will be held in County Square, with a fairground and face-painting for kids and an appearance by the St Mirren players should they win the cup.
Shops, cafes and pubs throughout the town have decked themselves out with black and white flags, scarves and posters, and a special beer – Buddy Bitter – has even been created for the game.
Carl Wengel, Houston Brewery's head brewer and lifelong Saints fan, was behind the creation. He said: "I'm very excited about this game and I decided to make a special beer for the pubs in Paisley. I'll have the biggest party if we win – it would mean everything to me."
Fraser Carson, 25, General Manager at The Bull Inn in Paisley said: " The council have given us an extension of our licence so we are open from 11 and we're starting early.
"We've got four buses running to the game – about 200 people will be leaving from here at Sunday lunchtime."
Paisley Rugby Club head coach Grant Sweenie, a long-time Saints fan, said: "As a club, we wish St Mirren the very best in tomorrow's final and we can't wait to join them in the town for the post-match celebrations."
Janet Osborne, from Renfrew said: "It would mean a lot for the town if we won.
"Hopefully, if they do, the flags will come out and some fireworks would be nice as well."
Lee-ann Redmond, 32, Uptown Barbers shop owner from Paisley said: " I'm looking forward to the game on Sunday.
"We've bought some spray paint for the fans hair, so we could do it white and black for Sunday before the game.
"It would be fantastic for the town and the fans. St Mirren fans are very loyal – whether they win or lose, they'll still support them and have a great day."