A federal judge in Dallas will sentence 42-year-old Phillip Amisano-Camillo later this year.
Prosecutors on Monday announced the plea deal — on the same day Amisano-Camillo's trial was scheduled to begin.
Amisano-Camillo pleaded guilty to enticement of a minor.
He originally was charged with enticement and travelling with intent to engage in sexual acts with a minor.
Investigators say Amisano-Camillo chatted online with the boy in April 2012.
In May 2012, he travelled from Washington state to Dallas, enticed the boy to sneak out of his home and had sex with the teen in a hotel.
Prosecutors didn't immediately provide Amisano-Camillo's hometown.