"Our marriage has been tainted with my infidelities," the 40-year-old told People. "I just want to be open and honest. I was irresponsible."
"I was associated with a woman who I was involved with and had a relationship with," Boreanaz said. "She asked for money. I felt as though I was being blackmailed or there was some sort of extortion."
Boreanaz has been married to Jaime Bergman for nine years and the couple has two children together: 8-year-old Jaden and 8-month-old Bardot.
"We're working on our marriage," he said. "We're working on repairing what has been damaged so badly."
Calls and e-mails to Boreanaz's rep were not immediately returned.