0402 GMT March 22, 2019
Frontrunner Zuzana Caputova, 45, was among tens of thousands of protesters who took to the streets of the eurozone country of 5.4 million last year after the killing raised concerns about media freedom and political corruption, AFP reported.
Opinion polls give the environmental lawyer and mother of two a double-digit lead over European Commission vice-president Maros Sefcovic, a 52-year-old career diplomat backed by the ruling Smer-SD party.
Caputova may have also got a last-minute boost after prosecutors charged a businessman believed to have ties to Smer-SD with ordering the murder of the journalist.
Yet, voters could interpret progress in the case as a sign of a functioning government.
Neither candidate is on track for an outright victory and a run-off vote for the largely ceremonial post is expected on March 30.
Caputova, a deputy head of the non-parliamentary Progressive Slovakia party, told AFP that "people are calling for change".
Journalist Jan Kuciak and his fiancée were gunned down in February 2018, just as he was to publish a story on alleged ties between Slovak politicians and the Italian mafia plus associated irregularities in EU farm subsidy payments.
The double murder and Kuciak's last explosive report, published posthumously, plunged the country into crisis.
Then prime minister Robert Fico was forced to resign but he remains the leader of the populist-left Smer-SD and is a close ally of current premier Peter Pellegrini.
Four people were charged last year with the killings. On Thursday, prosecutors announced they had also charged multimillionaire businessman Marian Kocner.
Kuciak had been investigating Kocner's business activities and had allegedly received threats from him.
"With this announcement, the authorities may have wanted to show just how effectively the state functions, so it could help Sefcovic gain some points," Bratislava-based analyst Grigorij Meseznikov told AFP.
"On the other hand, this could also be a vindication for Caputova, as she is the symbol of change."
Caputova has vowed to restore public trust in the state, running on a slogan of: "Let us stand up to evil".
Caputova has been endorsed by outgoing President Andrej Kiska.