The judge has reportedly decided not to join the results show following the death of his friend Stephen Gately.
Sara Lee, head of TV publicity at Hackford Jones PR which represents Louis Walsh, wrote on her Twitter page that he will not be on the programme tonight.
"To confirm Louis will not be appearing on tonight's X Factor," she said. "He thanks you all for the messages of support at this sad time."
Walsh had previously suggested that he would still appear as a judge as a tribute to Gately.
"Stephen was a massive fan of the show," a source told the News of the World. "When Louis and Stephen were together for the last time on Monday they spoke in detail about X Factor."
> Tributes flood in for Gately