In a surprise finish, 15-year-old Marlisa Punzalan has won The X Factor 2014.

The teenager from Mt Druitt, NSW beat 22-year-old Queensland crooner Dean Ray and folk-pop trio Brothers3 to the crown, securing a recording contract with Sony Music Australia.

Going into the final, which was screened over two nights and nearly five hours, Ray was the hot favourite, followed by Mudgee siblings Brothers3, but strong performances throughout the final saw Punzalan emerge victorious.

Early on, Brothers3 were sent home for the second time in the competition, having returned to the series via a publicly voted "wildcard" at the start of the live shows.

Punzalan and Ray were left to perform a song each - a personal "highlight" from the series so far - before a winner was announced.

X Factor and Australian Idol alumni Olly Murs, Guy Sebastian and Jessica Mauboy were special finale guests, performing with the finalists on Sunday night and solo on Monday night.

Mauboy dazzled with a vivacious performance of her new single Can I Get a Moment while Sebastian's new track Mama Ain't Proud featured American hip-hop star 2 Chainz rapping via video.

But the biggest star of all was Taylor Swift, performing current single Shake it Off from her new album 1989.

Asked if she had any advice for the finalists, the 24-year-old seven-time Grammy winner told them not to take anything for granted and to "be nice to everyone, not just the people you think can help you".

Punzalan, who claims to be so shy that most people at school didn't know her name pre-X Factor, chose Titanium by Sia and David Guetta for her final performance, while Ray sang George Ezra's Budapest.

Punzalan's win was the *second for mentor Ronan Keating in his five years in the role. The Irish pop star is due to commence a leading role in the musical Once the Musical in London's West End in November.

On Sunday night, part one of the finale was watched by 1.316 million nationwide, making it the most watched show on television. It was the highest ratings that The X Factor had delivered to date this series, with overall audience figures down 25 per cent on last series.

The end appears not to be nigh for the show yet, though; Channel Seven is already advertising auditions for next year's series.

*Correction: Brothers3 were not eliminated Sunday but last night, and Marlisa isn't Ronan's first win for the series.