Ward had initially made the final ten hopefuls for the 2002 talent contest, but quit the show after she felt that she was being exploited by producers.
She was later replaced by Nicola Roberts, who went on to make the final lineup of Girls Aloud.
Ward is said to have performed a cover of Mary J Blige's 'I'm Goin' Down' for the judging panel, where she said she "could still bring it", according to The Sun.
She later became one of the finalists chosen by Lord Andrew Lloyd Webber to represent the UK in the 2009 Eurovision Song Contest, but was eventually beaten by Jade Ewen.
Nicola Ward has also appeared on ITV1 dating series Take Me Out and Channel 5 talent show Don't Stop Believing.
The X Factor filmed auditions began in Liverpool earlier this month, with guest judges including Geri Halliwell, Leona Lewis and Rita Ora.
Watch former winner Matt Cardle talk to Digital Spy about the vacant X Factor spot below: