The vote will come just 10 days after one of the candidates - anti-corruption crusader and former lawmaker Fernando Villavicencio - was gunned down leaving a campaign event in Quito, highlighting a worsening security situation and prompting his erstwhile competitors to pledge to fight crime.
The new president will serve only until May 2025. Voters will also elect a new legislature and decide whether to allow oil development in a region of the country's Amazon and mining in a forest near Quito.
Here's a look at the top candidates:
LUISA GONZALEZ
Lawyer Gonzalez, 45, has pledged to bring back million-dollar welfare and social programs previously enacted by her mentor, former President Rafael Correa.
Gonzalez, who refers to herself a single mom, animal rights defender and sportswoman, has repeatedly evoked Correa's popular health, education and security policies and pledged to "recover the homeland."
The former lawmaker told Reuters she would use $2.5 billion from international reserves to shore up the struggling economy and invest in public infrastructure if elected.
She was leading voting intention with about 30% in recent polls, though no polls have been published since Villavicencio's killing.
Gonzalez has denied she would pardon Correa, who was convicted of corruption and sentenced to eight years in prison. The former president lives in Belgium.
YAKU PEREZ
Environmentalist Perez, who finished third in voting in the 2021 election, has said he will fight climate change and make agriculture, not oil, Ecuador's economic engine, winning him support in rural areas.
A lawyer who changed his first name from Carlos to Yaku, which means water in Quechua, Perez supports bans on oil development in the Yasuni reserve, in the Amazon, and on mining in the Choco Andino forest near Quito.
The 54-year-old widower has promised to fight crime with better social programs and data-driven security policies.
OTTO SONNENHOLZNER
Sonnenholzner, a 40-year-old businessman and economist, has promoted himself as a young policymaker seeking to bring "peace, money and progress" to Ecuador.
But Sonnenholzner's stint as vice-president under former leader Lenin Moreno - who is now facing bribery accusations - may hurt his chances to portray himself as a fresh start, analysts have said.
Moreno denies the allegations.
Sonnenholzner has promised a firm hand on security and to create jobs via private investment and sustainable growth of the dollarized economy.
JAN TOPIC
Topic, 40, a private security and telecommunications businessman, has promised security would be his first and most important focus if elected.
He says he served in the French Foreign Legion, most recently in Ukraine, and that technology and artificial intelligence could be used to combat crime.
Topic, who has no political experience, has said he admires El Salvador's President Nayib Bukele, who has taken a strong-man approach against gangs in the Central American country, but tried to distance himself from accusations of human rights abuses by Bukele's government.
CHRISTIAN ZURITA
Zurita, Villavicencio's replacement for the Construye party, is also an investigative journalist and has promised to honor Villavicencio's legacy by continuing to expose corruption.
If elected, he would better equip the police and enshrine intelligence protocols to fight crime, Zurita told Reuters, using international loans to shore up social programs.
"Until last Saturday I was a journalist," he said. "We do it for Fernando; we do it so his voice is not silenced."
Like his predecessor Zurita, 53, has also clashed with Correa, who sued the journalist over a book about the former president's brother's business dealings.
Already-printed ballots will show Villavicencio's name and photo, but the electoral authority has said votes will be counted for his replacement.
