"Kill Em with Kindness" was written by Selena Gomez, Antonina Armato, Tim James, Benjamin Levin and David Aude. The track was recorded by Steve Hammons and Adam Comstock at Rock Mafia Studios in Los Angeles, California. After adding the instrumentation and programming from Dave Audé, James and Blanco produced "Kill Em with Kindness" with assistance from R3drum. The song was sent to be mixed by Serban Ghenea at Mixstar Studios in Virginia Beach, Virginia. John Hanes served as the track's mixing engineer, and received assistance from Phil Seaford.

After releasing three successful singles from Revival, Gomez announced that she had begun recording a follow-up to the album, stating that she was ready to move on from the era. However, in an interview for 97.5 Now FM, Gomez revealed that "Kill Em with Kindness" was going to be released as the album's fourth and final single, saying: "‘Kill Em with Kindness’ is lyrically my favorite song I put on the record and I definitely can't wait to be able for that to have a story." It was serviced to contemporary hit radio on May 3, 2016. On May 31, 2016, the official cover art for the single was released. It features a lipstick print against a black surface, which Mike Wass of Idolator noted "vaguely ties in with the song’s message of rising above your haters."

Musically, "Kill Em with Kindness" is a groove-driven dance-pop song. Its electronic production is composed of airy synths, added bells, and a whistled hook, connected by a tropical breeze. Cristina Jaleru of The Washington Times called "Kill Em with Kindness" an "approachable dance track", while Mike Wass of Idolator noted that the whistle hook recalled Adam Lambert's "Ghost Town". According to the sheet music published at Musicnotes.com by Universal Music Publishing Group, the song is written in the key of B-flat minor with a tempo of 120 beats per minute in common time. The track follows a chord progression of B♭m – G♭ – D♭ – F7, and Gomez's vocals span from A♭3 to B♭4.

Lyrically, "Kill Em with Kindness" gives advice for dealing with critics, and delivers a message of choosing peace instead of violence and revenge. As the song opens, Gomez professes: "The world can be a nasty place / You know it / I know it". Wass noted the lyrics as conveying a message of peace, saying "instead of raising the proverbial middle finger, [Gomez] takes the high road." The theme of magnanimity is further displayed in lyrics such as "We don't have to fall from grace / Put down the weapons you fight with", imploring the listener to "put out the fire before igniting." According to Mikael Wood of the Los Angeles Times, the song was Gomez's response to "ungentle tabloid chatter" in regards to her health.

Tim Sendra of AllMusic picked it as a highlight from the album, remarking that "Gomez sounds most at home." Elysa Gardner of USA Today selected it one of the tracks to download and named it a "groove-driven, electro-savvy track." Sal Cinquemani of Slant Magazine noted that though it "lacks of originality," the song is yet a standout. James Reed of The Boston Globe called it a "dance-floor catnip," while Dave Hanratty of Drowned in Sound named it a "laser-focused sugar rush", adding that "Gomez succeeds in laying down a winning pop gauntlet." Mikael Wood of Los Angeles Times noted that "what's remarkable is how steadied she seems by such a facile conviction." Katharine St. Asaph of Time labelled it "au corant", which according to him "stirs a tropical-house breeze not dissimilar from Bieber's song 'What Do You Mean?'." Jia Tolentino of Spin wrote that the track works for addressing the viewing public, calling it a "hustling little posi-heater." Mike Wass of Idolator referred to it as a "triple threat's measured missive to haters," noting that the message "is a powerful stance in the age of online-bullying, Twitter beefs and messy open letters."