In August 2020, Shawn Mendes got the word "wonder" tattooed on his right arm, which would later turn out to be the title of the album and its lead single. On September 30, 2020, the singer took to his social media to tease towards the project with the caption "WHAT IS #WONDER". Hours later, he went on to announce the title and release dates of both lead single and album, as well as release the interlude "Intro", the first track on the album. The album pre-orders were released to streaming services on September 30.

In a statement, Mendes said of Wonder: "It really feels like a piece of me has been written down on paper and recorded into song. I tried to be as real and as honest as I've ever been. It's a world and a journey and a dream and an album I've been wanting to make for a really long time. I absolutely love it. Thank you for being by my side for so many years. I love you all so much."

To promote the album, a feature-length documentary titled Shawn Mendes: In Wonder directed by Grant Singer was released on Netflix on November 23, 2020, chronicling the past few years of Mendes' life, including his rise to fame, his 2019 self-titled world tour and the making of Wonder. Mendes executive produces the film, which was honored as a special selection at the 2020 Toronto International Film Festival.

Mendes revealed the album's tracklist through a Spotify canvas that was updated daily starting November 2, 2020. On November 13, Mendes revealed the tracklist on social media.

"Wonder" was released as the title track and lead single from the album on October 2, 2020. Teasers for both the song and accompanying music video were released alongside the announcement. "Monster", a collaboration with fellow Canadian singer Justin Bieber, was released as the second single on November 20. "Call My Friends" was released as promotional single alongside the album release on December 4.

Wonder debuted at number one on the Canadian Album Chart for Billboard, earning the highest sales and digital song downloads and the second-highest on-demand streams for the week. It became Mendes' fourth Canadian number-one album.

Wonder debuted at number one on the US Billboard 200 with 89,000 album-equivalent units (including 54,000 pure sales), becoming Mendes' fourth consecutive US number-one album. It made Mendes the youngest male artist and second-youngest artist after Britney Spears to top the Billboard 200 with four regular studio albums. It also made him the fourth-youngest artist in history to log four number-one titles on the Billboard 200. The album's tracks earned a total of 46.92 million on-demand streams in its first week. In its second week, the album descended to number 25 on the Billboard 200 dated December 17, 2020, with 28,300 units sold. It sold 30,000 units in the week dated December 24, 2020, on the Billboard 200.