The striker, 32, has barely had a look in at the Hawthorns this term, but has consistently scored goals throughout his career, moving from Luton to Arsenal as a youngster before playing for West Ham, Wimbledon, Coventry and Celtic.
At Parkhead, Hartson won three league titles before returning south of the border to West Brom. He has played 51 times for Wales, scoring 14 times, and remains an uncompromising centre forward.
The loan deal, agreed while Jim Duffy is in temporary charge following the demise of Peter Grant, runs for an initial month but could run until December 31st.