“This case is extremely poignant considering we are approaching the 25th anniversary of the Oklahoma City bombing,” Chief Wade Gourley of the Oklahoma City Police Department said in the statement. “This event not only scarred the community of Oklahoma City, but had a profound effect on the nation.”

Mr. Varnell’s lawyer, Vicki Behenna, said in an interview on Monday that the sentence was “a little bit higher than what we wanted” but that “we’re very grateful it wasn’t life, which is what the government was asking for.”

Ms. Behenna said that she planned to appeal Mr. Varnell’s 2019 conviction on counts of attempting to use an explosive device to damage and destroy BancFirst’s corporate offices, and of attempting to use a weapon of mass destruction against property used in interstate commerce.

Mr. Varnell’s arrest was the culmination of a domestic terrorism investigation involving an undercover operation, during which Mr. Varnell had been monitored closely for months as the bomb plot developed.

“This case required thorough investigation and careful coordination among agents and prosecutors in a matter that is our highest priority — terrorism,” said Timothy J. Downing, the United States attorney for the Western District of Oklahoma.