Malawi's President Peter Mutharika was sworn into office Saturday at a brief ceremony in Blantyre, the country's commercial center.
A larger inauguration is scheduled for Monday.
Mr. Mutharika was declared the winner of the election earlier Saturday by the national election commission. The election was marred by scattered unrest and complaints from the former president and others that the vote was rigged.
Mutharika, leader of the Democratic Progressive Party and brother of a president who died in 2012, won the May 20 election with nearly 2 million votes, or 36.4 percent of the electorate, according to the commission. Opposition leader Lazarus Chakwera came second with 27.8 percent, the election commission announced late Friday night. Malawi uses a first-past-the-post system, where the candidate with the largest share of votes, no matter how small a percentage of the total votes cast, is the winner.
President Joyce Banda was a distant third with just over 20 percent, according to the results. Ms. Banda had sought to annul the vote because of what she said were irregularities and had called for another election in which she said she would not participate, but a court said her move was invalid.
Banda came to power in 2012 following the death of Mutharika's brother, Bingu wa Mutharika.
Malawi is poor and heavily dependent on foreign aid. Banda initially drew praise for vowing to combat graft when she came to office, but her government has been tarnished by corruption scandals.
Justice Maxon Mbendera, head of the election commission, lamented the death of a young boy in post-election violence in the southern resort district of Mangochi. He urged Mutharika, a lawyer and former foreign minister, to "focus on what matters and to spend our taxes efficiently" and appealed to the losers to acknowledge that "there can only be one winner."
Jessie Kabwila, spokeswoman for Chakwera's opposition party, the Malawi Congress Party, said her party will challenge the results in court.
"We are disappointed because this is not a credible election," she said. "We can't have a president from a junk vote."
Nicholas Dausi, spokesman for Mutharika's party, said the victors would not be distracted by "bad losers."
Copyright 2014 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.