Joseph Hudak of Rolling Stone gave a negative review of the "Flatliner", criticizing it as "a hit that employs the laziest clichés of contemporary country music". He called the song "a step back for Swindell as a serious artist", compared to the maturity in the lyrics of previous releases "You Should Be Here" and "Middle of a Memory".
"Flatliner" first entered the Hot Country Songs at No. 36 on April 30, 2016 based on 14,000 copies sold when it was released as a preview track before the album You Should Be Here dropped. It only entered Billboard's Country Airplay at No. 48 on chart date of January 28, 2017 when it was released as a single, and re-entered the Hot Country Songs the following week at No. 48. It reached No. 10 on Hot Country Songs and No. 2 on Country Airplay in August 2017. The song has sold 280,000 copies in the United States as of September 2017.
The music video was directed by Michael Monaco and premiered in March 2017. It features Cole Swindell performing with Dierks Bentley at a show in Sioux Falls, South Dakota during Dierks' 2017 What the Hell World Tour.