Hervé Falciani, a 43-year-old French-Italian national who exposed the so-called Swissleaks scandal, has repeatedly said he would not travel to Switzerland for the trial and already failed to show for his initial court date last month, so his absence did not come as a surprise.
"I am not going," Falciani told reporters in Divonne-les-Bains, France, just a stone's throw from the border with Switzerland, last week, questioning the possibility of obtaining a fair trial.
The federal court in the southern Swiss town of Bellinzona noted as the proceedings opened around 8am Monday that Falciani was absent, the ATS news agency reported.
After a short recess, the trial resumed and will continue in his absence.
As a French national living in France, he cannot be extradited to Switzerland.
Falciani faces criminal charges in Switzerland for unauthorized data procurement, economic espionage and violation of business secrets, in addition to breaching Swiss banking secrecy laws.
The first witnesses in the case are due to be called to the stand on Tuesday, starting with the police officers who investigated Falciani's case and current and former employees of the HSBC Geneva branch.
One of his former girlfriends, who lives in Lebanon, also figures on the witness list, although it is not clear if she would show up.
Falciani leaked a cache of documents allegedly indicating that HSBC's Swiss private banking arm helped more than 120,000 clients to hide 180.6 billion euros ($205.4 billion) from the tax authorities.
He became an IT worker for HSBC in 2000 and moved to the bank's offices in Geneva in 2006.
The so-called "Snowden of tax evasion" and "the man who terrifies the rich" obtained access to a massive database of encrypted customer information, which was passed on to European fiscal authorities.
While he is viewed as a whistleblower and hero in countries where his leaked information is helping to net tax cheats, the Swiss authorities remain intent on prosecuting him.
Falciani has accused HSBC of pressuring Swiss authorities to move forward with the case against him.
Geneva prosecutors in June closed their investigation into HSBC's alleged wrongdoings after the bank agreed to pay tens of millions of dollars in compensation.
Geneva lead prosecutor Yves Bertossa at the time explained that "it is difficult to prove acts of money laundering. That is why we preferred to go with a negotiated solution."