After a four hour sentencing hearing in Bangor, Clarke was sentenced to 33 months on the robbery charge but to an additional seven years because he had brandished a gun during the heist.
Clarke pleaded guilty in January, 2007. A later attempt by his attorney to enter a new plea of guilty by reason of insanity was unsuccessful.
Clarke, a native of County Clare, was arrested after robbing a Bank of America branch in Bangor on October 4, 2006.
The robbery and arrest shocked family and friends in Ireland. Clarke was an award-winning student at Trinity College who had gone on to found his own software company.
Clarke, who has been held at the Cumberland County Jail in Portland, faced up to 25 years in prison. It had been expected, however, that he would be sentenced to a substantially lesser term given his lack of a previous record, his guilty plea and other factors. This turned out to be the case.
Clarke was apprehended shortly after the robbery while driving on Interstate 95. When detained he had $11,000, a loaded .38-caliber handgun and a box of ammunition.
Clarke had been living in Portland at the time of the robbery.
In passing sentence, Judge John Woodcock recommended that Clarke be placed in a facility where mental health care and treatment for drug and alcohol abuse would be available.
It has previously been reported in Ireland that Clarke was at one point diagnosed with schizophrenia.
Clarke has already served over a year and after serving about half his term in federal prison could be allowed serve the reminder of his sentence in Ireland.
Family and friends of Clarke, including his father and sister, attended the sentencing and there was emotional testimony delivered on behalf of the defendant as well as by a member of the bank staff.
Clarke showed no emotion as sentence was passed but his father, Michael, and sister, Michelle, were both in tears.
It will be several weeks before Clarke is assigned to a federal prison to begin serving the bulk of his time.
Judy Harrison of the Bangor Daily News contributed to this report.