X Factor judge Nicole will sing 'And I'm Telling You' alongside Sam Bailey, while Ellie will take to the stage with Luke Friend for 'Anything Could Happen' and Shane will perform Westlife classic 'Flying Without Wings' alongside Nicholas McDonald.
Sam, who is mentored by Sharon Osbourne, told the official website: "She's stunning, has the most spectacular voice and it will be an honour to share the stage with her. She has such soul when she sings and I couldn't be happier to duet with her."
Nicole mentored the girls category this year but none of her acts made it past the semi final stage.
Meanwhile, Luke admitted: "To perform with one of my favourite artists in the industry will be incredible, when Ellie sings you know exactly who it is she has such a unique voice. It's going to be an absolute honour."
He told Reveal earlier this week of rumours he'd be teaming with Ellie: "I don't know who it is but the rumours sound pretty cool. I've heard it's either Jessie J or Ellie Goulding, so it would be amazing if it is one of them because they're awesome. Obviously, I'll be busy rehearsing too. The final is going to be amazing."
Nicholas, who is also mentored by Louis, will join forces with Louis' old friend Shane, who helped the Irish judge pick his finalists at judges' houses. "It is such a big achievement and I'm overwhelmed and honoured to be singing with Shane as I've always been a massive Westlife fan," he said.
In addition to the duets, each finalist will perform another two songs.
Luke will sing 'We Are Young' by Fun' and 'What Makes You Beautiful' by One Direction, Sam will take on 'Power Of Love' by Jennifer Rush and 'Edge of Glory' by Lady Gaga, and Nicholas will sing 'Candy' by Robbie Williams and 'Angel' by Sarah McLachlan.
This week the trio will each visit their hometowns for a homecoming to be televised during the finale, which kicks off Saturday night on ITV.