"Where's Gilroy?" will appear on Kozelek's second album with Ben Boye and Jim White, which arrives next year.
The new song is Kozelek's response to the recent shootings in Gilroy, El Paso, and Dayton.
Kozelek released Mark Kozelek with Ben Boye and Jim White in 2017.
The Sun Kil Moon vocalist is also releasing another album with Petra Hayden titled Joey Always Smiled, which is due to land on 11 October.
In March of this year, Sun Kil Moon released their latest record I Also Want to Die in New Orleans.