"Bad Liar", described as a "slow-build pop rock tune", begins with a steady beat built around rhythm and an uneven bass-line from "Psycho Killer".
The track is written in verse-chorus form, although it features both a pre-chorus and a post-chorus.
Gomez worked with Canadian photographer Petra Collins for the single's promotional artwork.
The low fidelity video features Gomez wearing the same fall-risk wristband from the single's alternative cover art.
Gomez co-wrote the song with long-time collaborators Julia Michaels and Justin Tranter, and the producer, Ian Kirkpatrick.