The High Court case could run until Christmas, with the State strongly contesting Mr Bailey’s claims in his action for damages in relation to his alleged wrongful arrest in connection with the murder.
More than 80 witnesses, including two retired directors of public prosecutions, are expected to give evidence.
Ms du Plantier was murdered at her holiday home outside Schull in West Cork in December 1996.
Mr Bailey’s legal team has subpoenaed four senior legal officers to give evidence, including the two retired heads of the DPP — Eamon Barnes, who stepped down in 2000, and his successor James Hamilton, who retired in 2011.
The state solicitor for West Cork, Malachy Boohig, has also been called to give evidence, as has Robert Sheehan, a former senior lawyer with the DPP.
The DPP did not bring a prosecution against Mr Bailey in relation to the du Plantier case, with Mr Barnes later claiming the investigation was “thoroughly flawed and prejudiced”.
In 2001 Mr Sheehan wrote a strong critique of the Garda probe into the du Plantier murder, supporting Mr Bailey’s claims of innocence, but the document only emerged a decade later, around the time Mr Barnes sent an email to the DPP’s office claiming a “grossly improper attempt to achieve or even force a prosecutorial decision” by gardaí.
Another likely witness is Marie Farrell, a local woman who in 2005 dramatically withdrew her earlier statements which placed Mr Bailey close to the murder scene. She said she had been put under pressure by gardaí to implicate Mr Bailey.
The State will fight Mr Bailey’s action with witnesses likely to include retired Chief Supt Dermot Dwyer, who spearheaded the initial murder investigation, and retired Sgt Jim Fitzgerald.
Mr Bailey was arrested twice in connection with the case and is still the subject of a European Arrest Warrant, despite winning a Supreme Court appeal against any extradition attempt by French authorities also probing the murder.
Mr Bailey has said he was wrongfully arrested and was the subject of Garda efforts to pin the crime on him, an allegation denied by gardaí. His partner, Jules Thomas, has also sued for damages arising from her arrest in the murder investigation.
The civil action comes after a legal wrangle over access to tapes of phone calls related to the du Plantier case, recorded at Bandon Garda Station.