Ramos-Horta became prime minister after his predecessor, Mari Alkatiri, quit following last year's violence.
He also promised future oil and gas revenues and a new tax system that would benefit the poor in the tiny country gripped by poverty and youth unemployment that fuelled recent unrest.
Last year at least 37 people were killed in unrest following the soldiers' sacking.
About 150,000 people fled their homes in violence that led to the dispatch of an Australian-led international peacekeeping force to the country.
The renegade soldier's leader, Major Alfredo Reinado, is still being hunted by the international security force and is believed to have some popular support.
Security has been increased amid fears that violence could erupt during the election.
Other presidential candidates include Francisco Gutteres, the parliamentary head of the ruling Fretilin party and veteran politician Francisco Vaxier do Amaral, who lost to Gusmao in the 2002 race.
Gusmao has decided to retire from the presidency after being in power in East Timor since it formally became independent in 2002.
The country gained independence from Indonesia in a UN-administered referendum in 1999.