He served for a time as Congo-Brazzaville's Ambassador to Gabon and is a leading member of the Pan-African Union for Social Democracy (UPADS).
He also said that some expelled members had been rehabilitated for the sake of party democracy, and he stressed the party's stance towards the government of Denis Sassou Nguesso: "UPADS is firmly in the opposition, not to a man, much less to an ethnic group, but to a regime.
"[3] UPADS held its First Extraordinary Congress on 27–28 December 2006, electing Pascal Tsaty Mabiala to lead the party as its Secretary-General.
[5] Alongside Tsaty Mabiala, Gamassa participated in a May 2007 opposition rally in Brazzaville demanding the creation of an independent electoral commission prior to the June 2007 parliamentary election and threatening to boycott the vote otherwise.
[9] Gamassa, along with representatives from other UPADS factions, signed a declaration to reunify the party on 1 September 2010.