"If You're Not the One" received mixed reviews from contemporary music critics. On the positive side, Peter Robinson, in the
Gotta Get Thru This album review for the
NME, wrote "'If You're Not the One' [recalls] every chart-mauling uber-ballad you've ever heard". Nedd Raggett of
AllMusic commented in his album review "When it comes to ballads, they work best in sudden moments – the soaring end to 'If You're Not the One'".
About.com ranked the song at number 27 on its list of the 'Top 100
Pop Songs of 2002', two places behind the
album's title track. The song was again ranked at number 27 on the 2003 list, due to it being released in the United States during that year.
Music Week felt that the song showed Bedingfield's "sensitive side", and that the song "showcases his vocal range to stunning effect." The magazine even considered it "beautifully crafted." In his review for
musicOMH, Michael Hubbard was even less positive, stating, "'If You're Not the One' is as vomit-inducing as anything the man in the plastic mask has ever wretched
(sic) forth at the world". ==Chart performance==