Michael Francis Mara, 53, quietly answered "Yes, ma'am" or "No ma'am" but made no statement during a plea hearing before U.S. Magistrate Judge Hannah Lauck in Richmond. Mara will not be charged in other states.
Authorities say Mara took more than $83,000 in the heists, starting in Richmond in 2008 and ending with a North Carolina holdup the day before his Aug. 11 arrest. He was captured after a six-hour standoff with police at his Baton Rouge, La., home.
Mara faced up to 20 years for each charge, but his plea deal with prosecutors calls for him to spend 25 years in prison. He is scheduled to be sentenced May 11.
U.S. Attorney Neil MacBride said that while Mara has not given investigators any motive for the robberies, he was not "hard off" and was employed with a vehicle transportation company.
Mara's federal public defender, Elizabeth Wilson, declined comment following the half-hour hearing.
The FBI dubbed Mara the "Granddad Bandit" to help law enforcement and the public easily identify the suspect. The agency plastered bank surveillance photos of Mara on billboards around the country in August. He was arrested a week later after getting a tip from someone who saw the billboard.
Mara never used a disguise. He waited patiently in line and handed the teller a note demanding a specific amount of money. Once he suggested he had a weapon, but authorities said there was no indication he ever used one.
Mara typically reaped only a few thousand dollars at each bank, officials say. His largest take reported by authorities was $6,400 from a St. Louis bank in May 2010.
Officials say Mara began his two-year robbery spree in Richmond, but they didn't connect the dots until another holdup in Virginia last June. Prosecutors said Mara did not target banks in his home state and waited about a year to strike again in each state.
"He did take some steps to conceal his identity," MacBride said.
In court documents and at a detention hearing in September in Richmond, FBI agents said Mara confessed. After his arrest, agents found nearly $4,000 in cash in a black, zippered bag and about 15 "demand notes" written on deposit slips.
Mara had been set to go to trial for the two Virginia bank robberies in March.
In addition to the Virginia crimes, Mara acknowledged robbing banks in Alabama, Mississippi, Texas, Georgia, Arkansas, Kansas, Oklahoma, Tennessee, Kentucky, Missouri, New York, Florida and North Carolina. In court, he also acknowledged possessing an illegal weapon in Louisiana.