In what could be the biggest embezzlement case to hit the US Catholic Church, a Florida priest pleaded guilty on Wednesday to embezzling $US800,000 ($A1.21 million) of donations to fund a very unholy lifestyle.

John Skehan pleaded guilty to taking the money placed every Sunday into the collection plates to use instead on buying luxury homes, gambling trips to Las Vegas and buying rare coins.

His pleas came in a last minute twist as he and fellow priest Francis Guinan of the St Vincent Ferrer Catholic Church in Delray Beach were about to go on trial. He now faces up to 31 years behind bars.