Peter Mutharika was sworn in on Saturday as Malawi's new President after his arch-rival and predecessor Joyce Banda congratulated him and urged the country to move on from the disputed vote.
Mutharika, the brother of president Bingu wa Mutharika who died in office in 2012, appealed to the 11 other presidential candidates to "join me in rebuilding the country" after some -- including Banda -- contested the results.
Joining Vice President Saulos Chilima in taking the oath of office before a chief justice, Mutharika said he felt "very humbled" to stand as the fifth president of the impoverished southern African nation.
"It's obvious we are facing serious problems in this country. All of us together, let us build the country which is almost on the verge of collapse," Mutharika said in his first speech since being declared president late on Friday.
Conceding defeat earlier on Saturday, Banda congratulated Mutharika for his "victory in a closely contested election," according to a statement.
The results of the May 20 vote were announced on Friday minutes after the high court refused a last-ditch attempt to block their release and allow time for a recount.
The electoral commission said Mutharika took 36.4% of the votes cast against Banda's 20.2%, with the commission chief Maxon Mbendera declaring Mutharika "president-elect".
The results showed Banda beaten into third place by Lazarus Chakwera of the Malawi Congress Party (MCP), who garnered 27.8%.
Party spokeswoman Jessie Kabwila told AFP the MCP would challenge the results in court.
Banda, who became the country's first female president in 2012, had sought to have the polls declared "null and void" on the grounds of "serious irregularities".
But she made no mention of fraud as she issued a statement conceding defeat and urging the country to throw its weight behind Mutharika.
She said she wanted "to urge all Malawians to support the newly elected President Professor Mutharika and his Government as they take on this foundation of progress and endeavour to develop Malawi even further."
Banda described the elections as "tense," citing "isolated incidences of disturbances." One person was killed when police fired tear gas and rubber bullets at protesters demanding a recount in the southeastern town of Mangochi.
But she added that Malawians should move forward "as one nation, to remain united, to uphold the rule of law, and continue being peaceful and calm as we head into the next fifty years of Malawi's future."
Immunity from prosecution
Mutharika takes the reins of the country under the shadow of a treason charge.
The 74-year-old is accused of attempting to conceal his brother's death in office two years ago in an attempt to prevent Banda -- then vice-president -- from assuming power.
Banda prevailed and took office as decreed by the constitution, booting the former foreign minister out of the administration.
Mutharika, a law professor and former cabinet minister, faces additional counts of inciting a mutiny and conspiracy to commit a felony, along with other officials.
The trial is still pending, but analysts say it is likely the case will be set aside as Malawi's presidents enjoy immunity from prosecution as long as they are in office.
There is speculation that once Mutharika is in power he could turn the tables on Banda and have her charged with corruption over a $30 million graft scandal dubbed "Cashgate".
Banda has claimed credit for uncovering the fraud, which saw aid money siphoned into top government officials' pockets. But critics, including Mutharika, say the funds went into her party's election war-chest.