Jim Krapf was reinstated on Monday after the Chester fire commissioner granted an exception to a ban on locker decorations. U.S. flags are now allowed.
Commissioner James Johnson had instituted the ban in August after a controversy over a racially tinged cartoon that was posted on a locker.
Krapf was suspended without pay last week for refusing to remove his flag sticker.
About 40 people demonstrated at the fire station Monday in support of Krapf. The 31-year-old firefighter will return to work Thursday.