The 31-year-old Pacquiao, looking a little uneasy in an elegant formal shirt and leather shoes, pledged before about 1 000 spectators in Alabel in his southern Sarangani province to be a good, God-fearing civil servant.
"We can knock out any foe," the multiple world champion said, promising people in his impoverished province a "new chapter of our history."
Talking to reporters later, Pacquiao said he was nervous that he could not accomplish much but he promised to try his best to ease the widespread poverty gripping his province, about 1 000 km south of Manila.
"Entering politics is more daunting than boxing," he said.
It was a triumphant second try at local politics. He was soundly defeated when he first ventured into politics in a run for the powerful House of Representatives in 2007, but his worldwide profile has grown exponentially since then.
Aside from introducing bills during his three-year term that would provide livelihood for farmers and fishermen and benefits for athletes, Pacquiao has promised to help build a university and a hospital for the poor in Sarangani.
In a bid to show that he was serious at politics, Pacquiao recently took a ten-day crash course on legislation and governance.
A former baker and construction worker born to a poor family, Pacquiao became an embodiment of a rags-to-riches story in the Philippines where one-third of the 90 million people live on less than R8 a day.
Worshipped as a hero for bringing glory to a country beset with poverty, armed conflicts and political strife, Pacquiao has said he was ready to enter the ring a few more times before hanging up his gloves.
In a remarkable career to date, Pacquiao became the first boxer to win world titles in seven weight divisions. He is also regarded as the best boxer, pound for pound, in the world.
Promoter Bob Arum has been working to stage a fight between Pacquiao and undefeated Floyd Mayweather Jr, the other contender for the unofficial pound-for-pound title.