 After earning a master's degree in philosophy in Caracas and his doctor utriusque juris (Doctor of Canon and Civil Law) in the Dominican Republic, early in his professional career he served in various law firms in Trujillo, Mérida, and Caracas.He moved to Barinas in 1796 to practice law, and in 1807 was elected Mayor of Barinas.In 1810, Mendoza joined the insurgent movement started by wealthy Caracan citizens against the Spanish crown, and in 1811 was elected to represent the province of Barinas in the newly founded Constituent Congress of Venezuela.