"I have received this mandate from our people, from the nation, in an overwhelming demonstration of our people's commitment to democracy," he told reporters.
With 100% of the votes counted, Ramos-Horta had a strong lead with 62.09% of the votes, while Lu Olo had 37.91%, according to data from the election administration agency.
He was a co-recipient of the Nobel Prize in 1996 for his efforts to bring a peaceful resolution to a guerrilla war in East Timor against Indonesia's occupation of the former Portuguese colony. Ramos-Horta is one of East Timor's best-known political figures and served as president between 2007 and 2012 when he survived the assassination attempt by rebel gunmen.
Ramos-Horta is expected to be sworn in on May 20, the 20th anniversary of East Timor's restoration of independence.