Bieber was a presenter at the 52nd Annual Grammy Awards on January 31, 2010. He was invited to be a vocalist for the remake of "We Are the World" (a song written by Michael Jackson and Lionel Richie) for its 25th anniversary to benefit Haiti after the earthquake. Bieber sings the opening line, which was sung by Lionel Richie in the original version.
On March 12, 2010, a version of K'naan's "Wavin' Flag", recorded by a collective of Canadian musicians known as Young Artists for Haiti, was released. Bieber is featured in the song, performing the closing lines.
In January 2010, "Baby" was released from his debut album My World 2.0. The song featured Ludacris, and became an international hit. It charted at number five on the US Billboard Hot 100, peaked at number three on the Canadian Hot 100 and reached the top ten in several international markets. Two promo singles, "Never Let You Go" and "U Smile", were top thirty hits on the US Hot 100, and top twenty hits in Canada. According to review aggregator Metacritic, the album has received generally favourable reviews. It debuted at number one on the US Billboard 200, making Bieber the youngest solo male act to top the chart since Stevie Wonder in 1963. My World 2.0 also debuted at number one on the Canadian Albums Chart, Irish Albums Chart, Australian Albums Chart, and the New Zealand Albums Chart and reached the top ten of fifteen other countries.
To promote the album, Bieber appeared on several live programs including The View, the 2010 Kids' Choice Awards, Nightline, Late Show with David Letterman, The Dome and 106 & Park. Sean Kingston appeared on the album's next single "Eenie Meenie". The song reached the top ten in the United Kingdom and Australia, and the top-twenty of most other markets. On April 10, 2010, Bieber was the musical guest on Saturday Night Live. On July 4, 2010, Bieber performed at the Macy's Fourth of July Fireworks Spectacular in New York City. The following single from My World 2.0, "Somebody to Love", was released in April 2010, and a remix was released featuring Bieber's mentor Usher. On June 23, 2010, Bieber went on his first official headlining tour, the My World Tour, starting in Hartford, Connecticut, to promote My World and My World 2.0. In May 2010, Bieber featured in Soulja Boy's song "Rich Girl". In July 2010, it was reported that Bieber was the most searched-for celebrity on the Internet. That same month, his music video for "Baby" surpassed Lady Gaga's "Bad Romance" (2009) as the most viewed, and also the most disliked, YouTube video ever. However, Taylor Swift's video for her single "Blank Space" (2014) surpassed its number of views in 2015. In September 2010, it was reported that Bieber accounted for 3% of all traffic on Twitter, according to an employee of the social-networking site.
On My World 2.0, Bieber's voice was noted to be deeper than it was in his debut EP, due to puberty. In April 2010, the singer remarked regarding his vocals: "It cracks. Like every teenage boy, I'm dealing with it and I have the best vocal coach in the world ... Some of the notes I hit on "Baby" I can't hit any more. We have to lower the key when I sing live." Bieber guest-starred in the season premiere of the CBS American crime drama CSI: Crime Scene Investigation, which aired on September 23, 2010. He played a "troubled teen who is faced with a difficult decision regarding his only brother", who is also a serial bomber. Bieber was also in a subsequent episode of the series, which aired on February 17, 2011, in which his character is killed. Bieber performed a medley of his singles "U Smile", "Baby", and "Somebody to Love", and briefly played the drums, at the 2010 MTV Video Music Awards on September 12, 2010. Bieber announced in October 2010 that he would be releasing an acoustic album, called My Worlds Acoustic. It was released on November 26, 2010 in the United States and featured acoustic versions of songs from his previous albums, and accompanied the release of a new song titled "Pray".
Bieber's music is mainly pop and R&B. In 2010, Jody Rosen of Rolling Stone asserted that the content of his music was "offering a gentle introduction to the mysteries and heartaches of adolescence: songs flushed with romance but notably free of sex itself". In January 2012, Bieber told V magazine that he doesn't want to sing about sex, drugs and swearing. He stated "I want to do it at my own pace. I don't want to start singing about things like sex, drugs and swearing. I'm into love, and maybe I'll get more into making love when I'm older. But I want to be someone who is respected by everybody." But since then, Bieber gradually altered his artistry, with Peter Gicas of E! Online describing "PYD" as "sexed-up", while In Touch Weekly magazine describing his song with Maejor Ali and Juicy J "Lolly" might make his fans a bit uncomfortable because of its lyrics. After his hit in 2015 on Jack Ü's track "Where Are Ü Now", Bieber released the EDM-fuelled album Purpose a collaboration with Diplo, DJ Snake and Major Lazer.
In 2010, Bieber signed a deal with Proactiv. In the same year, Bieber partnered with Nicole by OPI to launch a nail polish line "The One Less Lonely Girl Collection", which sold exclusively in Walmart. Bieber's nail polish line sold one million bottles less than two months after its release. Bieber endorsed Adidas, beside Derrick Rose and Venus Williams, in 2012. He became the new "face" and "body" of Calvin Klein in early 2015. Entertainment Tonight reported that Bieber had used MYO-X, a dietary supplement, in preparation for the photo shoot. Bieber was criticized for "... hyping the latest 'miracle' supplement MYO-X, to his 59 million Twitter fans." In June 2015, Bieber teamed up with StarShop, a new shopping app launched by Kevin Harrington. Bieber endorses Beats By Dre, Elizabeth Arden and Best Buy. Bieber has been credited with boosting the careers of other singers such as Carly Rae Jepsen and Madison Beer when he tweeted about them.
Bieber was often featured in teen magazines, such as Tiger Beat, and has been labelled a "teen heartthrob". In 2010, he was frequently criticized for looking and sounding younger than his age, and the following year for an androgynous appearance, which had been commonly noted in the media, including his appearance on the cover of LOVE magazine's androgyny issue in 2011. His teen-pop music, image (especially as a heartthrob to girls), and the media attention he receives have additionally been criticized. He has been a target of Internet bloggers and message board posters, especially users of the Internet message board 4chan and of YouTube. Nick Collins of The Daily Telegraph said that "Bieber's character appears to strike a particularly sour note with his Internet critics" who have questioned his manner of speech, among other things.
Bieber's early fanbase developed on YouTube and predated the release of his debut album My World. According to Jan Hoffman of The New York Times, part of Bieber's appeal stems from his YouTube channel. Chicago Tribune noted that Bieber's fanbase, "Beliebers", was among the top words of 2010. Long before the November 2009 release of My World, his YouTube videos attracted millions of views. Braun recognized the appeal. Before flying him to Atlanta, Braun wanted to "build him up more on YouTube first" and had Bieber record more home videos for the channel. "I said: 'Justin, sing like there's no one in the room. But let's not use expensive cameras.' We'll give it to kids, let them do the work, so that they feel like it's theirs", recalled Braun. Bieber continues to upload videos to the same channel and has opened a Twitter account, from which he interacts with fans regularly; his account was reported to have more than six million followers in November 2010. Bieber surpassed Lady Gaga for being the most followed person on Twitter in January 2013. In early November 2013, Katy Perry surpassed him for having the most followers.
From December 2010 to March 2018, Bieber was in an on-again, off-again relationship with singer and actress Selena Gomez. In an interview on The Ellen DeGeneres Show, Bieber stated that some of his songs including "Sorry", "Mark My Words", and "What Do You Mean?" are about his relationship with Gomez.
Bieber supports Pencils of Promise, a charity founded by Adam Braun, the younger brother of Bieber's manager. The organization builds schools in developing countries, and Bieber became manager for the organization's campaign in Guatemala. He serves as a celebrity spokesman for the organization by running ads for the charity and its campaign "Schools4All". He promises to visit schools that donate the most funds to the organization. He takes part in the charity's fund-raising galas and donates parts of the proceeds from his concerts and Someday line of fragrances, and various merchandising to the charity. In 2010, Bieber supported a campaign for People for the Ethical Treatment of Animals (PETA) by urging fans to adopt abandoned pets from shelters. Bieber donated his hair to Ellen DeGeneres during his appearance in her talkshow The Ellen DeGeneres Show in March 2011. His hair sold on eBay for more than $40,000 and the proceeds was benefited the animal rescue charity, The Gentle Barn. Following the earthquake and tsunami in Japan in March 2011, Bieber donated proceeds from his concerts in Japan to Japanese Red Cross in May 2011. In December 2011, Bieber donated $100,000 to Whitney Elementary School in Las Vegas to provide students from low income families. Bieber supported Charity:Water, a nonprofit that brings potable drinking water to people in developing countries. On his birthday in 2011 and 2012, he launched his campaign to urge his followers to donate on Twitter. Bieber was named top charitable celeb of 2011 by American news aggregator and blog HuffPost.