The founding assembly was held on Saturday in Libreville, drawing over 10,000 supporters.
President Brice Clotaire Oligui Nguema described the UDB as a social-democratic party.
The party's rallying slogan is "Together, let’s build a New Gabon to be admired."
The UDB intends to present candidates in the upcoming legislative and local elections in three months, pending approval from the Interior Ministry.
The new party reportedly aims to break the long-standing dominance of the Gabonese Democratic Party (PDG), which ruled from 1961 to 2023.
"He [the president] sowed the seeds of a new country: Moral tranquility. Social justice. Respected secularism. Responsible ecology," said spokeswoman for the government Laurence Ndong, who was appointed president of the UDB Women's League.
