- Established as the Oromo National Congress (ONC) in April 1996
- Played a constructive role during the famously known Paris Peace Conference (opposition parties political conference), during the signing of tri-party agreement known as Joint Action for Democracy, and last but not least during that of the creation of the Union of Ethiopian Democratic Forces (UEDF)
In the May 2005 elections, in spite of all the obstacles that had been created by the regime:
- More than 4 million Oromos voted in support of ONC
- ONC won 105 seats in the Regional Council and 42 seats in the Federal Parliament
- UEDF won 52 out of the 547 seats in the Federal Parliament
- Forced to change its name from ONC to OPC in November 2007
- Formed a coalition with the Oromo Federalist Democratic Movement (OFDM) in January 2009. This coalition is named Oromo Federalist Congress (OFC), and OPC will be running under this ticket for the upcoming election.