The pair were spotted together at the Jalouse venue in Mayfair after Geldof attended the Vogue Gucci dinner in Chelsea, thelondonpaper reports.
An onlooker said: "The pair buried themselves in a VIP corner, but everyone could see that they were flirting wildly.
"Before long they ditched subtleties and began full-on snogging in full view of the entire club. Pixie showed no signs of slowing down, sweeping Noel back to Covent Garden with her party crowd."
A source told the Daily Mail: "They were sitting together at a table laden with Red Bull and spirits and were all over each other.
"She obviously found him really funny as they were both laughing and tickling each other."