It uses technology developed by online music firm PureSolo and charges users 99p per karaoke track download.
Users will be able to record their performances using free recording software on the service.
The is separate to , which carries a button advertising the sing-along service.
Robert Marsh, vice president of interactive and telephony at FME UK, said: "'The X Factor' is a brand that people truly want to engage with and PureSolo has delivered a fantastic online karaoke platform to enable this interaction."
Initially, the website will offer tracks performed in previous seasons and from the series six auditions.
Once the live shows start, backing tracks of the songs used in the programme will be made available as the show is airing.
The karaoke function will also offer built-in sharing facilities enabling users to burn tracks to a CD, download and store on MP3 players, e-mail to friends, and upload to a dedicated karaoke community for fans of the programme.
PureSolo chief executive David Kaplan, said: "We are thrilled to be working with FME to provide an easy and simple home studio recording facility which fits perfectly with 'The X Factor' philosophy of engaging its audience.
"While PureSolo aims to provide an educational resource and a platform for aspiring musicians and singers, part of our strategy is also to partner with businesses that have music engaged audiences, and this deal is completely in line with our vision for the company."
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