The detailed programme of the delegation's visit will be decided by the Conference of Presidents later on Wednesday.
The start of the mission was postponed for one day and is now expected to begin on Thursday.
It has now been confirmed that the two-day delegation will comprise members from different political groups and two committees - the civil liberties, justice and home affairs and budgetary control committees.
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On Thursday and Friday the delegation is due to meet with NGOs, journalists, senior members of the Slovak government and police.
For the Greens/EFA group, Hungarian MEP Benedek Jávor will be among those in Slovakia to probe the murder of investigative journalist Jan Kuciak and his girlfriend Martina Kusnirova.
The aim of the delegation is to investigate the crime, which, after the murder of Daphne Caruana Galizia in Malta, is the second murder of journalists who have investigated organised crime, corruption and tax issues.
The murder of Kuciak, 27, and his fiancée has shaken Slovakia like few other events since the country's independence in 1993. The young couple, who planned to get married in May, was murdered in the house where they lived east of Bratislava.
The Slovak President Andrej Kiska has said a “serious political crisis” has resulted from Kuciak's murder. He said he would host talks with the leaders of Slovakia's political parties to discuss his proposed government shake-up.
“I can see two solutions: a profound change to government or early elections,” he said.
Kuciak is thought to have been killed for investigating the Italian mafia's political influence in Slovakia.
The investigative journalist was working on a report highlighting the links between Slovakia’s political elite and the Italian mafia when he and his fiancée were shot dead in their home near Bratislava on 25 February.
Kuciak’s employer posthumously published his last article this week, which revealed ties between Slovak Prime Minister Robert Fico’s inner circle and people wanted in Italy for Mafia-related crimes.
Authorities subsequently detained several Italian businessmen named by Kuciak, but later released them due to lack of evidence.
Ahead of the delegation, German MEP Sven Giegold, Parliament's rapporteur on transparency, integrity and accountability of the EU institutions, spoke of the “unprecedented” speed with which the delegation had agreed to investigate the murders.
He said, “Never before has the European Parliament reacted so speedily to violations of fundamental rights in a member state.”
He added, “A 24-hour shift does not change that. Perhaps the Socialist Prime Minister in Slovakia will need a few more hours to clean up his office. More importantly, the European Socialist party family must finally distance itself unequivocally from Prime Minister Fico. The bashings against George Soros are just as intolerable as his insults to journalists. Fico is becoming the Orbán of Slovakia.”
He added, “Parliament must not stand idly by and watch the decline of the rule of law and freedom of the press in EU member states. This is not the place for party-political considerations. Organised crime and corruption are a growing threat to civil rights and democracy. Slovakia also needs to investigate tax fraud and misuse of EU funds.”