Kuciak's murder prompted huge street protests unseen since the 1989 anti-Communist Velvet Revolution and a major political crisis.
Slovakia's Supreme Court has dismissed a lower court's acquittal of a businessman accused of masterminding the 2018 killing of an investigative journalist and his fiancée.
It said the lower court did not properly assess evidence when it acquitted businessman Marian Kocner and one co-defendant of the murder of 27-year-old journalist Jan Kuciak and his fiancée, Martina Kusnirova.
Kuciak and Kusnirova were shot in February 2018 at their home in the town of Velka Maca, east of Bratislava.
Kocner had allegedly threatened the journalist following the publication of a story about his business dealings. Kuciak had published nine stories about the businessman.
The case concerning Kocner will now return to the Specialised Criminal Court in Pezinok, which acquitted him in September.
At that time the court's judge said there was not enough evidence to convict. Prosecutors appealed the verdicts to the Supreme Court hours later.
Former soldier Miroslav Marcek pleaded guilty to shooting Kuciak and Kusnirova and was sentenced to 23 years in prison in April 2020.
Prosecutors had alleged Kocner paid Marcek to carry out the killings.
The couple's deaths prompted major street protests unseen since the 1989 anti-Communist Velvet Revolution and a political crisis that led to the collapse of Slovakia's government.