The 52 year old with an address at Monkstown Grove, Co Dublin faces up to ten years in prison after pleading guilty to 14 theft and deception charges dating from 2003 to 2008.
Among his victims was a County Tipperary farmer.
Breifne O'Brien went all the way to the Supreme Court to try stop his trial.
He claimed too much adverse publicity meant he would not receive a fair hearing but lost that battle in May.
Last month on the day his trial was due to start he pleaded guilty to 14 sample counts of theft and deception.
The businessman now admits defrauding 5 individuals out of millions of Euro in a scam likened to a ponzi scheme
Friends and associates including Carrick on Suir farmer Louis Dowley and businessman Evan Newell were duped into investing in bogus property, shipping and insurance deals here and in places like Paris and Hamburg.
The sentencing hearing before Judge Patricia Ryan is expected to go on all day.
