Rachel Sonis of "Idolator" defined it as "a jazzy, soothing, coffee shop-ready number that sticks to the album's 'quiet moments in life' theme", noting similarities to Adele's melancholic approach and praising the song for "show[ing] off his precious pipes more than ever before." Following the success of their breakthrough single "Stay with Me", "I'm Not the Only One" found chart success in several countries. In the United Kingdom, the song entered the UK Singles Chart at number ninety-three, when the album was released on the week of 1 June 2014, before it re-entered at number sixty-nine on the week of 10 August 2014. It kept climbing the charts in the following weeks until it reached a peak of number three on the week of 14 September 2014. By reaching number three, the song became the album's third top-three hit for the singer, whose last two singles from the album reached number-one. In Ireland, the song reached number six, becoming their third top-ten hit. In Europe, the song also reached the top-ten in Denmark, Italy and Netherlands. In the United States, "I'm Not the Only One" shared similar success. It debuted on the "Billboard" Hot 100 at number sixty-nine, during the same week where "Stay with Me" was in the top-ten and "Latch" was reaching the top-twenty. It later reappeared at number ninety-three, and within four weeks the song climbed to number twenty-five, becoming that week's biggest gain in digital sales. The following week, the song reached number twenty, marking their fastest flight to the top-twenty (seven weeks) among his four entries. Four weeks later, the song climbed to number nine, thus earning Smith their third top-ten single in the same year (2014). With three top ten singles, Smith became the only male to achieve the feat in 2014 and the third overall artist with the most top ten singles of 2014, along with Iggy Azalea, who also scored three, and behind Ariana Grande, who had four. It eventually peaked at number five, becoming their second top-five hit. In Australia, the song failed to reach the top-ten by one position, reaching its peak at number eleven, ending their streak of consecutive top-five singles, but in New Zealand the song peaked at number three, earning their second consecutive top-three single. In both countries, the song was certified 2x platinum by the Australian Recording Industry Association and the Recorded Music NZ respectively.