The singer said that she would not agree to sit on the panel because she couldn't be "mean" to the contestants.
Asked if she would consider a guest judging stint on the programme, Boyle told Digital Spy: "I'm not sure I'd make a very good judge. I couldn't be mean to people."
In her first Twitter chat on the social networking site this morning, the star also quipped that Ronan Keating "would make a nice stocking filler" this Christmas, and told this year's Britain's Got Talent winner Jai McDowall: "I wish you all the best, you're great."
The show is currently looking for a new judge after comedian Michael McIntyre announced his departure after just one series.
Susan Boyle's third studio album Someone To Watch Over Me is out now.
Watch Susan Boyle perform a cut from her new album 'Autumn Leaves' on The X Factor Australia below: