Partial official results on Monday showed Berger had a nearly insurmountable lead over opponent Alvaro Colom.
With 94% of the vote counted, Berger led Colom by 54% to 46% in the race to succeed President Alfonso Portillo on 14 January, the Supreme Electoral Tribunal said.
Following the announcement, Berger called on Colom to concede and join him in moving the nation forward.
"Let us all come together to make the changes this country needs," the 57-year-old candidate of the Grand National Alliance said.
"Let us all come together to make the changes this country needs"
But a spokesman for Colom's party said the National Union of Hope standard-bearer would not comment until after all votes are counted.
Ramiro McDonald said party leaders "are reviewing all the information we have obtained... and simultaneously we are analysing the data that the Supreme Electoral Tribunal gave."
Five million people were eleigible to vote, but election officials said turnout was only 46%.
Neither of the two conservative businessmen received a majority in the 9 November first round, forcing a runoff.
However, the vote eliminated former dictator Efrain Rios Montt from contention, to the relief of many Guatemalans who consider him a human-rights abuser.
Rios Montt, accused of genocide during his brief rule from 1982-1983, had also drawn international attention to the race. He backed Colom in the runoff.
Berger, 57, pledged to abide by the 1996 Peace Accords that ended Guatemala's 36-year civil war.
More than 200,000 people were killed or went missing during the war, 80% of them indigenous Mayans, according to the UN-backed Truth Commission.
Former US President Clinton expressed regret for America's role in the war, saying that Washington "was wrong" to have supported Guatemalan security forces that slaughtered thousands of civilians.
The former mayor has also promised to "fight hard against discrimination and racism" and to promote intercultural values.
Alvaro Colom (R) has not yet to
He pledged earlier to include Mayans in his government as tourist information officers. But Indian leaders dismissed those as domestic jobs - the kind many Mayans already have in wealthy Guatemalans' homes.
Meanwhile, Colom, 52, claimed to be better equipped for the job of turning Guatemala into a multicultural society.
He is the only non-Mayan ever to qualify as a spiritual leader in Guatemala's ancient native religion.
The textile magnate got into politics in 1999 as presidential candidate of the New National Alliance, which also included demobilised leftist guerrillas of the National Guatemala Revolutionary Unit.
A year later, he founded his current party and shifted his ideology toward the centre.