"Angel" was McLachlan's second consecutive top five hit on the Billboard Hot 100 chart, debuting at number twelve, and then jumping to the top ten the following week, before peaking at number four. It remained at the top ten for nineteen weeks, and for twenty-nine weeks in the top 100. "Angel" was the eighteenth most successful song of 1999.
"Angel" was one of the first songs written for Surfacing. McLachlan said that writing it was easy, "a real joyous occasion." It was inspired by articles that she read in Rolling Stone about musicians turning to heroin to cope with the pressures of the music industry and subsequently overdosing. She said that she identified with the feelings that might lead someone to use heroin: "I've been in that place where you've messed up and you're so lost that you don't know who you are anymore, and you're miserable—and here's this escape route. I've never done heroin, but I've done plenty of other things to escape." She said that the song is about "trying not to take responsibility for other people's problems and trying to love yourself at the same time".
The song has a sparse arrangement — mostly McLachlan at the piano, with subtle upright bass played by Jim Creeggan of Barenaked Ladies. It was recorded in the key of D-flat major. For live performances, it is transposed up one half-step to D major and played without the bass.
A remix of the track by Dusted appears on McLachlan's 2001 album Remixed.
Since 2007, "Angel" has been included in an advertisement for the American Society for the Prevention of Cruelty to Animals (ASPCA) in which McLachlan serves as the spokesperson. The song is played over video of dogs and cats in an animal shelter and is credited with helping raise millions of dollars for the ASPCA.
The song was also donated by McLachlan for Tribe of Heart's movie The Witness which depicts the awakening of consciousness of a New York City construction worker with respect to the treatment of animals.
The teenaged pop-opera Italian trio Il Volo performed this song for their 2nd PBS TV Special, We Are Love in 2013.
Marti Pellow covered this on the album Love to Love in 2011
Live cover performances
In 2004, Australian Idol contestant Hayley Jensen performed this song on the first week of the semi-finals of the second season and was voted through to the Final 12 the following night. Jensen eventually recorded a cover for that season's Finalist Cast Album.
In 2006, Angel was performed on the fourth season of Canadian Idol on the first week of the semi-finals by eventual winner Eva Avila. Avila recorded a cover of the song for that season's Top 10 Cast Album.
The song was performed by Katherine Jenkins at the opening ceremony of the 38th Ryder Cup in Wales, on the 30th of September 2010, in front of an estimated TV audience of over 600 million. She also performed the song as a part of a tribute to Sports Personalities who had died in 2010 at The 2010 BBC Sports Personality of the Year Ceremony on the 19th of December 2010, at The LG Arena in Birmingham.
Prince covered "Angel" during the European "20Ten" Tour in July 2010, and during the Welcome 2 America Tour Jan 2011.
On June 14, 2011, the American The Voice contestant and eventual winner Javier Colon performed it in the first season of the show. The studio version peaked at number 64 on the Billboard Hot 100.
On June 22, 2013, The Voice of the Philippines contestant Lee Grane performed the song during her blind auditions. The performance trended world-wide on the micro-blogging site Twitter and received a million views on YouTube.