The Filipino, 37, has won more than 15.5 million votes with over 96% of voting precincts counted and was in seventh place out of 12 winning senators.
Earlier this year, he said he planned to retire from boxing to become a full-time politician.
Run your race the best that you can, no matter the result. pic.twitter.com/v1XBABCfOf
— Manny Pacquiao (@mannypacquiao) May 15, 2016
The Christian boxer has made headlines in the past for making contraversial comments about same-sex couples.
In February Filipino was accused of making a homophobic slur, he said homosexuals as "worse than animals" in a television interview.
He said: "It's common sense. Do you see animals mating with the same sex?''
"Animals are better because they can distinguish male from female.
"If men mate with men and women mate with women they are worse than animals," Pacquiao said when his comments were translated into English by TV5's Facebook page.
He apologised to people hurt by his comments but made clear he opposed same-sex marriage.
Jesus tells us in John 15:12
— Manny Pacquiao (@mannypacquiao) May 14, 2016
"This is my commandment, That ye love one another, as I have loved you." pic.twitter.com/2EhkejCp5d
Pacquiao comes from an impoverished family and worked odd jobs before trying boxing aged 12.
He is now one of the world's most celebrated and wealthiest athletes.
The Philippines is an overwhelmingly Catholic country and Pope Francis paid a visit in 2015.
Pacquiao is up against the controversial Filipino presidential hopeful Rodrigo Duterte.
Mr Dutere said he wanted to ask 'forgiveness' from the Pope earlier in the month for criticising him during his visit last year.
He also made headlines when he 'joked' about an Christian Australian missionary that was raped and murdered in his city.
36-year-old Jacqueline Hamill was killed in 1989.