“This is the dawn of a new era," Bio said in a speech Wednesday after winning the run-off election.
"The people of this great nation have voted to take a new direction," he added at a short ceremony during which he appealed for national unity.
Bio's chief opponent was Samura Kamara of the All People's Congress (APC), which has a majority in parliament, and the campaign was bitter and tainted by allegations of fraud.
"There is no doubt that there is significant division, that the campaign was a difficult one, or certainly a tense one," Luisa Enria, a lecturer in International Development at the University of Bath, told RFI.
Kamara has already vowed to contest the outcome, citing alleged irregularities that delayed the official announcement of the result, which gave the APC candidate 48.19 percent and Bio 51.81 percent.
Fraud concerns aside, Enria argues that Bio's Sierra Leone People's Party (SLPP) has gained traction.
"If you compare these results with the 2012 results, SLPP has gained quite significant increase and margins in all districts," she said.
Most notably in Sierra Leone's diamond-rich district of Kono.
"We’ve seen some swings and then we’ve seen some votes that went to smaller parties, in the first round, being redistributed to the SLPP in the second round," Enria points out.
"What I’m worried about is: Did they vote for Maada Bio or did they vote against the APC?" says Mamuna Camapo-Maiyo, who runs a community project with the Sierra Leonean diaspora in France.
After years of civil war and a deadly Ebola outbreak, public discontent with the outgoing Koroma administration was high and may have helped the SLPP win.
"It's not all the fault of the APC government," explains Enria, but "there were some policy decisions that for some people made things more difficult."
One of those was an austerity programme that was put in place immediately after the end of the Ebola outbreak that killed some 4,000 people.
"I think economic hardship was tangible for a lot of people in Sierra Leone," she says.
Diaspora welcomes Bio win
Meanwhile, in the diaspora news of Bio's victory has been met with relief.
"I'm very excited, happy and relieved," Camapo-Maiyo told RFI. "It’s been a long process. I was worried about the security of my family and the people of Sierra Leone in general. A small thing can lead to a big event."
Several episodes of violence were reported at political rallies this year, and at least one death and several injuries were recorded.
"What I was worried most about is the social media," continues Camapo-Maiyo, in reference to the spread of fake news on the internet and the release of results before the official announcement.
But Camapo-Mayo is not convinced that Bio will bring real change.
"He has been in government before but let's see," she comments.
Bio is no stranger to Sierra Leonean politics.
He took part in a military coup in 1992 and briefly ruled the country four years later, before handing over power to a civilian government.
He has promised not only to reunite the country but also to improve people's everyday lives, notably by providing free eduction for all.
Turning the economy around
But he will need to come up with the money first.
"He's going to have to clamp down on corruption within the government sector to produce some revenues," reckons Jamie Hitchen, a Sierra Leonean political analyst.
Despite posting double digit growth in 2012, the west African country is one of the world's poorest.
"There are question marks about how much of that GDP growth was filtering down to improve the everyday reality for ordinary Sierra Leoneans," cautions Hitchen. "But now there’s an increase in food prices, there’s a lack of jobs. It’s a very difficult economic situation to manage."
Sierra Leone's reliance on mineral exports does not help either, given the global slump in commodity prices.
"A lot of the candidates talked about diversification of the economy, moving towards agriculture, tourism, fisheries," Hitchen told RFI. "These things are all going to take a bit of time; it’s going to require some patience."
But patience may not be on offer.
The country needs "free education for children and to create jobs because we have so much potential, agriculturally, in Sierra Leone. There’s a lot to be done," says Mamuna Camapo-Maiyo.
Expectations are high and Bio will be judged on his ability to deliver.
The fact that the SLPP does not have a majority in parliament could provide an opportunity reckons Enria.
"The opposition will be there to ensure that Maada Bio keeps his promises and is held to account," she said.