The guilty plea makes Fullwood, a Jacksonville Democrat, ineligible to serve in the Legislature and will force his party to find a replacement candidate for the Nov. 8 elections.
Fullwood's attorney, Robert Willis, said the lawmaker pleaded guilty to one count of wire fraud and one count of failure to file an income tax return. The other 12 counts of the indictment, which was unsealed in April, will be dismissed as part of an agreement with prosecutors. Sentencing is scheduled for Jan. 9.
The maximum sentence for each count of wire fraud is 20 years, with one year the maximum term for the tax return charge.
His trial was set to begin Oct. 11.
Under the original indictment, Fullwod faced more than 200 years in federal prison, though as a practical matter first-time offenders rarely face anything like the maximum sentence.
The plea deal came less than a month after Fullwood narrowly beat back a primary challenge from Tracie Davis, who lost to Fullwood by less than 3 percentage points.
Democratic Party leaders will select a replacement candidate for the November vote.
According to the indictment, from at least September 2010 to about December 2011, Fullwood electronically transferred money from the "Reggie Fullwood Campaign" bank account to an account of a Fullwood-owned entity called Rhino Harbor, LLC. Prosecutors said he used the money for personal use at grocery, jewelry and liquor stores.
To conceal the embezzlement of campaign funds, the indictment alleged that Fullwood submitted fraudulent campaign expenditure reports to the state.
Florida law requires state candidates' campaign accounts to be separate from personal accounts. The campaign money also may not be used to defray normal living expenses, other than for transportation, meals, and lodging that is campaign-related.
Fullwood, 41, was first elected to the House in 2010 and was re-elected without opposition in 2012. He served as Democratic deputy whip from 2012 to 2014.
His time in the House was interrupted in 2014 when his seat became vacant after paperwork errors prevented him from qualifying for the ballot. Fullwood returned to the House in February 2015 after winning a special election.