In 2009, Mercer and producer Danger Mouse formed the side project Broken Bells, for which they released a self-titled album in March 2010, followed by After the Disco in 2014, and then Into the Blue in 2022.

"[5] He attended the University of New Mexico and studied chemistry for a time before dropping out, saying that although he enjoyed the subject matter, he was not cut out for it because his head was "too in the clouds for stuff like that.

In 2007, Mercer sang backup vocals on the tracks "Florida," "Missed the Boat," and "We've Got Everything" on Modest Mouse's album We Were Dead Before the Ship Even Sank.

Mercer has been credited with playing several instruments on The Shins' albums including guitar, bass, synthesizer, ukulele, banjo, harmonium, and percussion as well as beat and MIDI programming.

In 2010, Mercer acted in Matt McCormick's feature film Some Days Are Better Than Others, playing the role of Eli, a directionless slacker.

[12] Also, in 2010, Mercer and Modest Mouse frontman Isaac Brock contributed original music to director Chris Malloy's 180° South, a documentary about adventurers in Patagonia.

"[13] Musical influences he has mentioned include The Smiths,[4] The Cure,[4] Echo & the Bunnymen,[4] The Beatles[4] and Orchestral Manoeuvres in the Dark (OMD).