The TV stars fell out during filming for The X Factor's fourth series in 2007 and have not seen each other since the show's final.
According to the Daily Star, both women have now told Cowell that they will be attending his 50th birthday celebrations in Wrotham Park, Hertfordshire this weekend.
A source said: "All eyes will be on them. Let's hope they make their peace for Simon's big Five-O."
Music manager Sharon quit The X Factor's judging panel last year and went on to blame Dannii for her departure. She also described the Australian singer as an "iceberg" who wanted "to f**k Simon Cowell".
Meanwhile, Minogue has insisted that her former colleague's attacks show "what kind of person she is".
A spokesman for Osbourne said: "Sharon will be one of 500 guests at this party. I doubt she and Dannii will even meet."