He was vice president from 2006 to 2018 to Ellen Johnson Sirleaf, Africa's first elected female president, who rebuilt a ravaged Liberia after a civil war left an estimated 250,000 dead.
It is Boakai's second and likely last run for the top job — he already lost to President George Weah in a 2017 run-off.
The two face off again in a second round vote on Tuesday, following last month's hard-fought first ballot, in which neither secured an outright win.
Boakai has castigated the record of his opponent, a former international star footballer, and emphasized his own experience in office, proposing a "rescue plan" for the West African country.
He has pledged to improve infrastructure, invest in agriculture, attract investment, open the country to tourism and restore Liberia's reputation.
"His motivation is to rescue Liberia from the current state it is in," Mohammed Ali, Boakai's Unity Party spokesman told AFP.
He highlighted an "influx of illicit drugs, the increase in the poverty rate (and) the image of the country being so low" as problems that have worsened under Weah's presidency.
His strategy seems to be working.
While six years ago Boakai won 28.8fi in the first round and 38.5fi in the second, he pulled level with Weah in this year's first round, with both receiving about 43 percent of the vote.
Alliances
Boakai has promised an inclusive government, reflecting the country's political, ethnic, regional, religious and gender diversity.
Some of the 18 other candidates who are now out of the race, such as Tiawan Gongloe, have endorsed him.
FILE - Then - Liberian Vice-President Joseph Boakai and Presidential Candidate of the Unity Party, centre, arrives to cast his votes during a Presidential runoff election in Monrovia, Liberia, Tuesday Dec. 26, 2017.
In the first round, he skillfully built alliances with local political leaders, such as the former warlord Prince Johnson, who supported Weah in 2017 and still enjoys strong support in his native Nimba County.
An ally of Johnson — now a member of the Liberian Senate who is under U.S. sanctions for corruption and was seen in a 1990 video sipping beer while his soldiers torture and kill president Samuel Doe — is Boakai's running mate.
Their ticket won easily in the heavily populated northeastern region.
Like 57-year-old Weah, Boakai is from the Indigenous population and not the US-Liberian elite, who founded the free nation and were descended from slaves.
He was born in a remote village in Lofa County near the borders with Guinea and Sierra Leone, often called Liberia's "breadbasket."
He was agriculture minister from 1983 to 1985 under Doe.
Boakai portrays himself as a simple man who rose from humble origins through hard work. He is married with four children.
Age and credentials
Throughout the campaign, his team has presented Boakai as a man of integrity whose credentials make him the only candidate able to tackle corruption — one of Weah's key 2017 promises and one on which some voters say he has failed.
"He believes in perfection, he takes note of everything," his senior advisor Augustin Konneh told AFP.
"Boakai is a very humble person."
His opponents argue his age is a handicap, suggesting he is out of touch in a country where 60 percent of the population is under the age of 25.
Rather than aspiring to run the country, they say it's time to retire and have nicknamed him "Sleepy Joe."
"He has built a coalition with different factions," Ibrahim Al-bakri Nyei, director of the Ducor Institute for Social and Economic Research said.
"Should he win the election, it will be a major challenge for him.
"There are huge expectations for all the members of the coalition."