The 63-year-old Wrenshall admitted, in response to a prosecutor's questions, to detailed graphic abuse of boys as young as 4 years old.
Wrenshall, a thin, bespectacled, balding man with grayish-white hair, wore a bright yellow prison jumpsuit and told the judge that he had two graduate degrees.
He then acknowledged conspiring to engage in sex tourism and soliciting clients in the U.S. and elsewhere to visit his home, where he arranged for them to have sex with prepubescent boys from 4 to 12.
He admitted to encouraging his clients to photograph, videotape, and share footage of the exploits.
Assistant U.S. Attorney Lee Vartan says authorities discovered Wrenshall was running a brothel for pedophiles in Thailand after confiscating computers from Wayne Corliss of Union City, N.J.
Wrenshall was extradited from Thailand after authorities found correspondence and chat room conversations between the two men, and others.
Vartan read from e-mails that Wrenshall acknowledged he had sent to Corliss.
"'I am ready, willing and able to be your guide,"' Vartan read from the e-mail. "'Boys are available here."'
The e-mails outlined the prices for sex acts on children, and encouraged clients to bring certain items from the U.S., including "lots of bubble bath," that Wrenshall said were hard to buy in Thailand.
Corliss, a small-time actor and former children's entertainer known for playing Santa Claus, is serving a 20-year sentence in a New Jersey prison. His 2008 arrest was the culmination of an international manhunt. He admitted traveling to Thailand three times from 2000 to 2002 to have sex with at least two boys, ages 6 and 9.
Seven people have been arrested in the investigation, which is ongoing, according to Vartan.