The delayed vote on Tuesday pits George Weah, a 51-year-old ex-international football star and Liberian senator, against 73-year-old Joseph Boakai, who has served as vice president under President Ellen Johnson Sirleaf for the past 12 years.
A total of 5,390 polling stations across the country opened their doors for 2.1 million registered voters at 08:00 GMT. Polls will close at 18:00 GMT.
Both Weah, the candidate for the Congress for Democratic Change (CDC), and Boakai, of the Unity Party, have promised to revive Liberia’s struggling economy and kick-start infrastructure projects.
The two ranked first and second respectively in the October 10 first round – Weah won 38.8 percent and Boakai 28.8 percent – but neither secured the 50 percent needed to win outright.
“Many Liberians feel that these are very crucial elections and that they need to cast their vote,” said Al Jazeera’s Mohammed Adow, reporting from a polling station in Liberia’s capital, Monrovia.
“Many of them have even postponed their Christmas celebrations to ensure that they vote today,” he added.
Christmas, the holiday marking the birth of Jesus Christ, is celebrated by most Christians on December 25 in the Gregorian calendar. In many of these countries, December 26 is also a public holiday.
Initially scheduled for November 7, the run-off was delayed after the party of a third candidate filed a legal complaint alleging voter fraud and irregularities.
Liberia’s Supreme Court ultimately cleared the way for the vote to take place on Tuesday.
On the campaign trail, Weah promised to lower poverty levels by creating jobs in both infrastructure and agriculture.
He also said a CDC government would consider paying exam fees and using a sector-wide review to bolster Liberia’s weak education system.
Weah is using his popularity as a sports icon to garner votes with Liberian youth, a large demographic. Roughly 60 percent of Liberia’s population is under 30.
Jewel Taylor-Howard, a senior senator and ex-wife of former President Charles Taylor who is serving a 50-year sentence for war crimes, is running as Weah’s running mate.
The platform of Boakai’s Unity Party hinges on prudent economic decisions and infrastructure.
Road construction is his flagship issue.
“When you have roads, all other things can happen,” Boakai said during campaigning, while also promising to create 50,000 jobs in his first 150 days in office.
If the runoff goes smoothly and the results are accepted by both parties, it will be the first peaceful transition of power in Liberia in more than 70 years.
Sirleaf, the incumbent president, has made it clear that she wishes to hand over power to a democratically elected president when her time in office comes to an end on January 15, 2018.
In 2011, Sirleaf was a joint recipient of the Nobel Peace Prize for her “non-violent struggle for the safety of women and for women’s rights to full participation in peace-building work” in the wake of Liberia’s two bloody civil wars, which spanned 14 years before ending in 2003.
Analysts say the eventual winner faces a tough road ahead.
“The lack of trust that the Liberians have in their institution is due to the pervasive corruption that unfortunately the Sirleaf administration has not been able to completely stem,” Alix Boucher, assistant research fellow at the Africa Center for Strategic Studies, told Al Jazeera.
“The challenges start from the lowest level of interaction with the state and the winner is going to have to deal with that. It’s going to be very difficult,” she added.