Posting a jokey picture of herself pretending to throttle Cowell, she wrote: "GUESS WHAT!! I'm baaaacccckkkkk!!!!#iMayActuallyRingHisNeck #XFactor2014 #leggooo."
Simon Cowell welcomed her comeback, calling the Girls Aloud singer "a brilliant judge of talent".
The pair fell out in 2011 after Cowell sacked Cole from the American version of the show after only three weeks as a judge.
She filmed one episode before being dropped by Cowell and the incident soured relations between the pair.
Cole was reportedly let go because of fears that her accent would not be understood by American viewers.
She did not return to the UK X Factor either and was replaced by Tulisa Contostavlos.
Cole and Cowell are both confirmed to be judges in the next X Factor series but the rest of the line-up is not yet known.
The remaining members of the judging panel will be announced in the coming weeks, ITV said.