Mamboundou announced the UPG's establishment in Paris on 14 July 1989, during the single-party rule of the Gabonese Democratic Party (PDG).
However, his candidacy for the December 1993 presidential elections was rejected, resulting in party supporters rioting in Libreville.
Mamboundou was the UPG candidate in the 1998 presidential elections, finishing second behind incumbent Omar Bongo with 16.5% of the vote.
Although most opposition parties boycotted the December 2011 parliamentary elections, the UPG participated, losing all eight seats.
[1] On 11 September 2015, President Ali Bongo Ondimba appointed Dieudonné Moukagni Iwangou, a hardline opposition leader and UPG faction leader, as Minister of State for Agriculture in an effort to incorporate the opposition into the government, but Iwangou refused to accept the position.