After signing a record deal with Island Records in June 2014, Mendes released his debut single "Life of the Party" which peaked at number 24 on the US Billboard Hot 100. Following the single release, an EP titled The Shawn Mendes EP was released on July 28, 2014, and sold 48,000 copies in its first week. Mendes announced his debut album title and artwork on January 27, 2015 and it was made available to pre-order on February 2, 2015.
Handwritten was reissued in a revisited edition on November 20, 2015. It includes five live recordings tracks from the Greek Theatre and four brand new songs.
"Life of the Party", was released as the lead single from Mendes debut EP The Shawn Mendes EP on 25 June 2014. The song serves as the first single from Handwritten as well. A one-shot lyric video for the song showing Mendes in the George Street diner premiered on Vevo on June 30, 2014. The official music video for the song premiered on March 10, 2015.
"Something Big", was released as the album's second single on November 7, 2014. The official music video for the song premiered on November 11, 2014 on Vevo, and it is Mendes' first official music video.
"Stitches", was released as the album's third and final single on May 5, 2015. The song debuted on the Billboard Hot 100 chart of June 13, 2015, at number 89 and became his first top 10, peaking at number 4. Peaking at No. 1 in the UK Singles Chart being Mendes' only number 1 in the UK to date.
"I Know What You Did Last Summer", was released as a single from a revisited edition of the album on November 18, 2015. The song is a collaboration with Cuban-American singer Camila Cabello. It has peaked at number 20 on the Billboard Hot 100 chart. In the UK the song peaked at number 42.
Before the album release, Mendes released five songs through pre-order on iTunes. The first song "A Little Too Much", was released on February 2, the same day the album pre-order started. A music video for the song premiered on the singer's Vevo on February 4. Mendes announced through Instagram that the second promotional song would be "Never Be Alone" and it was made available on February 16. An official music video for the song was released on February 25. On March 16 the singer released "Stitches", the third pre-order single, which official music video premiered on March 18. An acoustic version of "Life of the Party", featured in the deluxe version of the album, was released as the fourth pre-order single on March 30 at midnight, the same day as it was made possible to hear every song preview on iTunes. "Kid in Love", was made available as the fifth and final pre-order track on April 6 at midnight, just a week before the album release, while a music video for the acoustic version of "Life of the Party", was posted on Shawn Mendes' Vevo on April 10. "Aftertaste" also gained a music video, which was posted on April 17.
The album debuted at number one on the US Billboard 200, selling 119,000 album-equivalent units in its first week, of which 106,000 copies were pure album sales. He became the youngest artist since Justin Bieber to have a No. 1 album on the Billboard 200 album chart in nearly five years. Bieber was 16 years and 2 months old when his album My World 2.0 spent its fourth and final week at the top. Mendes was 16 years and 8 months old. In its second week, the album descended to number seventeen with 20,000 equivalent album units, of which 12,000 copies were pure album sales, an 89% pure album sales decrease (from 106,000 copies), surpassing Madonna's MDNA (2012) for the biggest second-week percentage drop for a number-one debuting album in the Nielsen SoundScan era. As of August 2016, Handwritten has sold 391,000 copies in the United States.
In his native Canada, the album debuted at number one with first-week sales of 14,000 copies, according to Nielsen SoundScan. In its second week, the album descended to number six.
Handwritten has received mixed reviews from music critics. At Metacritic, which assigns a "weighted average" rating out of 100 from selected independent ratings and reviews from mainstream critics, the album received a Metascore of 58, based on 5 reviews.
Billboard's editor Carl Wilson stated "confident hooks and big dynamics make the syrup go down smoothly", talking about the singles "Life of the Party" and "Stitches," and the blue-eyed-soul track "I Don't Even Know Your Name", noting the latter influenced by Justin Timberlake and Bruno Mars. Writing for The Guardian, Caroline Sullivan rated the album three-out-of-five stars and claims: "At 16, Mendes isn’t the artist he’ll be at 25, but he’s made a persuasive start – the adult-pop big league could yet be his." Nick Murray from Rolling Stone described Mendes as a "nice-guy guitar strummer more influenced by the light acoustic pop of Ed Sheeran."