Businessman Breifne O'Brien has pleaded guilty to 14 sample counts of deception and theft at the Circuit Criminal Court in Dublin.
Mr O'Brien, who is 52 and lives in Monkstown in Co Dublin, was charged with 45 offences of deception and theft involving sums totalling around €11 million.
Lawyers for the Director of Public Prosecutions said his guilty pleas were acceptable on the basis that the full facts surrounding all the offences would be heard at the sentencing hearing.
The counts related to inducing investments in bogus property deals in Manchester, Paris and Hamburg, as well as investments in a bogus "linen shipping insurance scheme" and theft.
The case will be mentioned before Judge Patricia Ryan next week, when a date will be set for sentencing.
Lawyers for Mr O'Brien said he had no previous convictions.
Defence Counsel Patrick McGrath asked for time to allow a probation report to be prepared.
He said that although these were very serious matters and the judge may have no alternative but to take a certain course when it comes to sentencing, the court may benefit from such a report.
Judge Ryan said she would not order a probation report at this stage and suggested the sentencing hearing may be held before the end of July.
Prosecuting lawyers said the sentencing would take around a day.
Luán Ó Braonáin said it would be a "complex matter" involving the "interweaving of various strands of evidence".
Mr O'Brien had taken two legal challenges to try to halt his trial.
Last month, the Supreme Court ruled the trial could proceed despite his claims that he would not be able to get a fair trial because of adverse publicity.
A second challenge based on a recent judgment relating to the rights of people in garda custody to have solicitors present during interviews was dismissed by High Court President Mr Justice Nicholas Kearns earlier this month.
The 14 counts to which Mr O'Brien pleaded guilty today relate to deceiving and stealing from five individuals: Louis Dowley, Pat Doyle, Evan Newell, Martin O'Brien and Daniel Maher.
Some of them have already been granted judgments against Mr O'Brien in the Commercial Court.
It heard in 2009 that Mr O'Brien told solicitor, Brian Quigley, that he had been living a lie for up to 15 years in relation to investments made for other people, some of whom had been long-time friends.