The 43-year-old, who previously appeared as a judge on Channel 5's Don't Stop Believing, posed with Tulisa backstage and had a go on some bagpipes to celebrate arriving in Scotland.
Anastacia has sold over 20 million records worldwide and scored six top 20 hits in the UK between 2000 and 2004 when she released the albums Not That Kind, Freak of Nature and her self-titled third LP.
She is the sixth guest judge of this X Factor series, following Mel B, Geri Halliwell, Nicole Scherzinger, Leona Lewis and Rita Ora.
A full-time fourth judge will have to be announced by the end of the summer when the show films its Judges' Houses stage of the competition.
X Factor auditions finish with dates in Cardiff and Newcastle later this month.