[6] "Mercy" was serviced to US top 40 radio stations as the second single from the album on October 18, 2016.

Writing for Rolling Stone, Joe Levy noted "Illuminate mixes professions of romantic agony like "Mercy" (where a quietly hummed hook explodes into crashing drums), with nice-boy valentines like "Treat You Better" and bedroom come-ons like "Lights On"" while naming the album "disarmingly intimate.

"[15] Jon Reyes of Idolator, wrote that "[Shawn's] most noticeable change, aside from the tight music hall sonics, is the subtle infusion of sex into the lyrics" as well as feeling that the record as a whole "displays his lyrical development" and "polishes a proven formula.

"[16] Stephen Thomas Erlewine of AllMusic wrote that the album has "a bit of grace and warmth" and that Mendes "came into his own on Illuminate while also complimenting his "small and sweet" voice and how he "has gelled into his pop persona.

"[14] Sonia de Freitas, writing for Renowned for Sound, noticed that it "is apparent that Mendes has shifted to a more mature and soulful sound, and far more introspective lyrical content" while praising his vocals, writing that "he sings earnestly, with an emotive delivery in every song.

"[17] Billboard listed the track "Don't Be a Fool" at number 90 for the best deep cuts from 21st century pop stars.

In addition, Mendes is the first artist to have their first two full-length studio albums hit number one since 5 Seconds of Summer bowed at number one with Sounds Good Feels Good (2015) and their self-titled debut album (2014), and the first male artist to claim the distinction since 2015, when ASAP Rocky bowed atop the list with At.

Illuminate also picked up 3.8 million audio on-demand streams, the second highest total of the week, trailing only Drake's Views.