Theresa Villiers declined to divulge how many extra troops would be deployed for the two-day summit next month, but said military assistance would be used to back up the police.
"At the request of the PSNI and in line with standard military aid to civil authority, yes the military will be providing assistance to the PSNI as is normal with events of this scale," said Ms Villiers.
Army helicopters will be used to fly world leaders and their entourages to and from the event at the Lough Erne golf resort outside Enniskillen.
However, the Secretary of State refused to be drawn on further details of the army's role.
The leaders of the world's eight wealthiest countries are expected in Fermanagh on 17 and 18 June.
PSNI chief constable Matt Baggott said that he expected thousands of protesters to descend on Northern Ireland during the G8 Summit.
"We are expecting demonstrations in Belfast and we are expecting some in Enniskillen as well. I would anticipate thousands. There are many routes into Northern Ireland," he said.
Meanwhile, G4S - the firm behind the Olympic security fiasco - is also to provide support at the summit.
The company suffered a multimillion pound loss and damage to its reputation after failing to provide all of its contracted guards to the Olympic Games in London last year.
G4S will supply 450 employees to the event.
Ms Villiers said lessons had been learned and claimed that the UK Foreign Office was confident G4S could deliver.
"The G8 is considerably less than the numbers that were required for the mammoth operation at the Olympics," she added.