The Movement for Socialism (MAS) party, holding a congress in the eastern city of Montero, approved the candidacy of Morales.
The Movement for Socialism (MAS) party, holding a congress in the eastern city of Montero, approved the candidacy of Morales -- Bolivia's first president with an indigenous background -- in a unanimous vote.
Morales welcomed the party's decision, saying, "If the people decide it, Evo will continue."
He added: "So many times we have defeated the right."
Morales was first elected president in 2005, and re-elected in 2009 and 2014.
But he narrowly lost the referendum in February on the question of whether he was constitutionally permitted to run again in 2019. His current term expires on January 22, 2020.
The party congress Saturday, however, recommended "four legal alternatives" to allow his candidacy within the constitutional framework, according to a union leader who read the conclusions.
The first was a partial constitutional reform through an initiative requiring the signatures of some 20 percent of the electorate; the second also involves a constitutional reform to allow an extended presidential mandate.
The third recommends that the president renounce his office before the 2019 elections, so that he would not have served three full terms; and the fourth involves a reinterpretation of the constitution.
Morales, who has cultivated an "everyman" image, has been highly popular through most of his presidency.
He won his first election with 54 percent of the vote; his second with 64 percent and his third with 61 percent.
Morales has generally benefited from a fragmented opposition.
At the time of the February referendum, his popularity had been damaged by allegations that he had fathered a child with a young woman, Gabriela Zapata, and done favors for the Chinese company employing her.
He admitted the two had had a son, who died in infancy, but emphatically denied the other allegations.
In a survey early this month, the Ipsos polling firm found Morales's popularity was still relatively solid, at 49 percent.