Skehan faces charges with fellow priest, the Rev Francis Guinan, originally from Birr, Co Offaly, who has pleaded not guilty. Prosecutors say the pair took cash from the offering plate at St Vincent Ferrer Catholic Church, in West Palm Beach, and stashed it in the church ceiling and in offshore bank accounts.
They then spent the money on expensive homes, gambling trips to Las Vegas with a mistress, even a $275,000 (£200,000) rare coin collection, authorities say.
Both are charged with stealing hundreds of thousands of dollars, although church auditors believe the total amount taken could be in the millions.
Police reports say Skehan used $134,075 to pay for his alleged lover's expenses, gave $11,688 to relatives and used another $268,630 for personal expenses such as dental work and credit card payments.
Authorities said Mr Guinan had had an "intimate relationship" with a former bookkeeper at a church where he previously worked and used church money to pay her credit card bills and her child's school fees. They also said she accompanied him on holidays.
Mr Skehan had previously pleaded not guilty but changed his plea on Wednesday.
"Father Skehan accepted responsibility for his actions by virtue of his guilty plea," Scott Richardson, his lawyer, said outside the court. "It's been extraordinarily difficult for him from the beginning."
The scandal broke in 2006, stunning parishioners at the seaside parish.
Mr Skehan, who had been at the church for 40 years, is accused of taking $370,000 between 2001 and 2006, the timeframe covered by the statute of limitations. Auditors think he actually stole more than $8 million over 20 years.
Mr Guigan, 66, is accused of stealing $488,000 during the 19 months after he became pastor in Sept 2003. He is due to stand trial on Feb 18.
Mr Skehan will be sentenced on Mar 20. Both face up to 30 years in jail if convicted.
After the investigation began, Mr Guinan begged the church to stop the audit and "call off the dogs". In a letter released by prosecutors, he said that priests "devote their lives to the church with little thought for personal gain".
Richard Barlow, Mr Guinan's lawyer, said his client had done nothing wrong and that his co-defendant's plea did not affect his case. He said he would prove Mr Guinan spent the money on church business.