According to sources, the two ladies are in "final negotiations" with the network and just working out the odds and ends before making their additions to the show official.
Rowland -- who judged The X Factor's U.K. version in 2011 -- and Rubio's deals will reportedly be set in stone within the next couple days.
A Fox representative declined comment.
Rowland and Rubio would be replacing two-time judge L.A. Reid and second-season judge Britney Spears on the reality singing competition's third-season panel.
Us Weekly reported late last month "Kelly's nearly a done deal" and Fox is also considering actress Jennifer Love Hewitt and country star Reba McEntire.
Lovato announced her return to the show in late March. Reid announced in December he won't be returning toThe X Factor after serving on the panel for two seasons, while Spears confirmed in January she had "made the very difficult decision" not to take on another edition of the series. According to reports, both parties opted to quit the show before Fox could fire them.
Fox announced last month Khloe Kardashianwill not return to host the show. The network formalized her departure with an announcement in which they revealed Kardashian's fellow first-time The X Factor co-host Mario Lopez will return as "the host" of the show's third season.