Pacquiao accepted the nomination of his PDP-Laban party at its national convention on Sunday, saying that the Filipino people have been waiting for a change of government.
"I am a fighter, and I will always be a fighter inside and outside the ring," Pacquiao, 42, said in his speech.
"I wholeheartedly, bravely, and humbly hope for your support," he added.
Pacquiao is the president of the PDP-Laban faction led by him and Sen. Aquilino "Koko" Pimentel III.
Another faction of the same party earlier this month nominated President Rodrigo Duterte to be its vice presidential candidate, and Duterte's former aide, Sen. Bong Go, as its presidential nominee.
Duterte, who is forbidden by the constitution from seeking a second six-year term, has accepted the nomination, but Go has declined to run for president.
Duterte has led a brutal campaign against illegal drugs, and said last week he would rather "die first" before facing an international tribunal, the day after the International Criminal Court announced it would investigate allegations of crimes against humanity linked to the crackdown that has left thousands dead.
Pacquiao has accused the administration of Durterte, his former ally, of making corruption worse in the Philippines.
To critics who question his qualifications, the former boxer has said his personal experience of poverty will better equip him to lead the nation. He added that he will fight poverty and corruption.
"In my whole life, I have not backed down on any fight," Pacquiao said.
He warned politicians that he holds responsible for corruption "will soon end in jail together."
The rival party faction supporting Duterte earlier said it will petition the Commission on Elections to declare Pacquiao and his allies illegitimate officers of the ruling party.