Former PriceWaterhouseCoopers employees Antoine Deltour and Raphael Halet are facing up to five years in prison for forwarding 28,000 pages of internal documents to journalist Edouard Perrin, who has also been accused of complicity in the case.
The decision, to be handed down in the Criminal Court of Luxembourg, will be closely watched as it touches on a range of key issues currently being debated in Europe and across the globe.
The explosive 2014 revelations revealed the extent as to how more than 300 multinational corporations, including Pepsi, Ikea, Amazon and tech giant Apple, negotiated secret deals with the Luxembourg government to avoid paying taxes on profits made in Europe.
The scandal triggered huge debate about the issue of tax evasion and so-called "sweetheart" deals, which combined with the Panama leaks of earlier this year, prompted the European Union to announce greater measures aimed at improving financial transparency.
Whistleblower Protection
While the issue has triggered widespread debate about tax evasion and loopholes for multinational corporations, it has also spawned a debate about the protection of whistleblowers.
Supporters have called for Deltour and Halet to be given immunity for their parts in the LuxLeaks scandal, arguing that their intervention was in the public good.
Tense day for #luxleaks #whistleblowers, verdict expected at 3. Live updates here. pic.twitter.com/qDtQC0tyNR
— Greens in the EP (@GreensEP) June 29, 2016
There is also pressure from the European parliament, with Deltour receiving the parliament's citizens' prize and was praised by the EU's competition commissioner Margrethe Vestager.
"Luxleaks could not have happened if it was not for the whistleblower, and the team of investigative journalists," she told the news website EurActiv earlier this year.
#Luxleaks trial verdict today: #whistleblowing is not a crime! Sentence for Deltour would strongly discourage others to publish information
— ECPMF (@ECPMF) June 29, 2016
"The two worked very well together to change the momentum of the debate about corporate taxation in Europe. I think everyone should thank both the whistleblower and the investigative journalists."
However, the pair face the prospect of time in prison, accused of theft, secrecy violation and wrongfully accessing a database, with some critics calling for the whistleblowers to face punishment for their actions in accessing and releasing the sensitive documents.
Today is a crucial day for #whistleblowers: #LuxLeaks verdict expected at 3pm CEST. #SpeakUp @TI_EU https://t.co/xzx7u4M28W
— Transparency Int'l (@anticorruption) June 29, 2016
The case also has parallels to that of former NSA whistleblower Edward Snowden, who is potentially facing a lengthy prison term after releasing documents that revealed the widespread surveillance practices of the US government.
Snowden, who is currently living in exile in Russia, has gained international support as activists are calling for him to be exonerated from any investigation and charges.