"I swear to God and I promise the people to faithfully comply with the Constitution and the laws of Colombia," Petro, 62, said during the Sunday ceremony.
After his inauguration, Francia Marquez was sworn in as vice president of Colombia during the same ceremony.
In June, Petro declared victory in the presidential race over businessman Rodolfo Hernandez with 50.51% of the votes. During his pre-election campaign, Petro said that it was necessary to normalize ties with neighboring Venezuela that were severed in 2019 under Petro’s predecessor Ivan Duque.
Petro, who is a former guerilla and ex-mayor of Bogota, is the first leftist leader in Colombia’s modern history. He has promised to solve the problem of poverty and to redistribute the tax burden on more affluent residents.