The suspect, who authorities have identified as 50-year-old James Matthew Kenny of Cumming, died at a Texaco on Ga. 9 near the Midway community.
The incident happened about 10 minutes after Kenny reportedly held up a nearby Wachovia bank.
Forsyth County Sheriff Ted Paxton said the suspect was shot after a "confrontation" with a deputy.
"He pulled the wrong day and the wrong place to pull this stunt," Paxton said.
Two sheriff's deputies, whose names have not been released, have been placed on administrative leave with pay, Paxton said.
The Georgia Bureau of Investigation is handling the shooting probe.
Paxton credited "constant training" that deputies go through for their ability to handle the incident.
"Even though this is a rare event for us, in this line of work there is no way to predict when and where this kind of thing is going to happen," he said.
Authorities have not confirmed whether Kenny, who was traveling alone, fired on either of the deputies.
No one else was injured at the bank or gas station. Investigators found an undisclosed amount of money and other evidence from the robbery in the van.
The robbery and shooting unfolded quickly Monday afternoon.
Kenny was driving a white work van that witnesses said had left the bank on Bethelview Road, where an armed robbery had been reported about 1 p.m.
Officials with Wachovia could not be reached for comment.
Nancy Parks said she was the lone customer inside the bank when a man entered wearing sunglasses and a piece of cloth that covered his head.
"He walked in and went right to the next teller and that's when he pulled the gun and jumped over the counter," Parks said. "He told the girl he wanted the money ... he grabbed a bunch of money, jumped back over the counter and went right out."
When the man went over the counter, Parks said she turned her head so that he wouldn't see her looking at him.
"I just acted like I wasn't paying any attention to him," she said, adding that the teller saw the man leave in a van.
About 10 minutes after the robbery, a sheriff's deputy reported that he was behind the van. He followed it to the gas station a couple miles south of the bank, where another deputy joined him.
At that point, Paxton said, Kenny got out of the van with a weapon in his hand. Deputies repeatedly told him to drop the gun before shots were fired.
Authorities closed off the gas station until about 4:30 p.m.