"It's taken more than a decade, but I'm delighted to finally be on a panel with three girls (I think!). Paulina and Kelly both have great taste and massive experience in the music industry and together with Demi, this is going to be a fun panel. It just feels like the time to do something different," Cowell said in a statement.
Rowland -- who judged The X Factor's U.K. edition in 2011 -- and Rubio will be replacing two-time judge L.A. Reid and second-season judge Britney Spears on the reality singing competition's third-season panel.
"I am very excited to be reuniting with Simon Cowell and The X Factor family," said Rowland. "It feels great to be able to take this journey here at home in the states!"
"I love The X Factor!" added Rubio. "I can't wait to find the next big music star here in America. "I'm so thrilled to be part of the show as a judge. Simon, be careful what you wish for, let's see if you are ready to handle me, empieza la fiesta, amigo!"
TMZ reported on Monday Rowland and Rubio were in "final negotiations" with Fox to mentor the upcoming season's contestants with Cowell and Lovato.
"We are thrilled that Kelly and Paulina are joining Demi on the panel this season, in what is sure to be a triple threat of talented and successful women against Simon week-to-week," Fox reality chief Mike Darnell said in a statement. "This is an incredible panel of judges and we can't wait for fans to see what's in store for Season Three of The X Factor."
"Kelly's incredible talent as a member of one of the world's most successful groups, Destiny's Child, combined with her judging experience as part of the U.K. version of The X Factor, make her an ideal choice to join this talented panel," added The X Factor executive producer Trish Kinane.
"Paulina is an amazing Latin superstar who brings glamour and fiery passion to the judges' table. We welcome both of them in joining Simon, Demi and Mario in what will prove to be an exciting season."
Lovato announced her return to the show in late March. Reid announced in December he won't be returning to The 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.