John Darwin, 57, admitted obtaining money by deception and obtaining a false passport.
Darwin made headlines in December when he walked into a London police station claiming to have amnesia. He had been declared dead after disappearing while canoeing off the English coast in 2002.
Police accused Darwin and his wife, Anne, of staging the death to collect his $50,000 insurance policy. British newspapers ran pictures that appeared to show the couple in Panama, four years after John Darwin's alleged death.
Darwin admitted seven deception charges and one passport offense during Thursday's hearing at Leeds Crown Court in northern England. He denied nine other charges of using criminal property. Prosecutors said he would not be tried on those charges.
Darwin's attorney Peter Makepeace said his client had been seen by a psychiatrist but there were no mental health issues relevant to the case.
"Mr Darwin has been in custody," Darwin's attorney Peter Makepeace told the U.K. Times. "It has been an extremely difficult time for him. There has been self-harming issues."
"He accepts entirely that a lengthy custodial sentence is inevitable," he said.
Anne Darwin, 55, pleaded not guilty to 15 charges of deception and using criminal property. Her trial is scheduled to start in July.
Detectives said the couple's two sons, Mark and Anthony Darwin, were never told that their father was still alive and were innocent "victims" of the plot. They have since disowned both their parents reports the Times.