The 28-year-old was signed by previous City boss Brian Tinnion in July 2005 in a £150,000 deal from Motherwell.
Tinnion was sacked two months later and Partridge fell out of favour following the appointment of Gary Johnson.
The Wales international was loaned out to MK Dons during the second half of his first season at Ashton Gate and had loan spells at Leyton Orient, Brentford and Swindon last term.
Robins manager Gary Johnson told the club's official website: "We hope this allows Dave to get his football career back on track and we give him and his family our best wishes for the future."
Sporting Life