Authorities allege the 19-year-old deliberately lit seven fires on the far south coast of New South Wales — the state worst-hit by a recent spate of devastating bushfires — between mid-October and late November.
The man was allegedly seen sitting in a vehicle on Tuesday afternoon shortly before a fire broke out nearby.
“Police will allege in court that the man lit the fire and left the area before returning to respond to the fire as part of his duties as a volunteer firefighter,” police said in a statement.
He was arrested shortly afterwards and charged with seven counts of causing a fire and being reckless to its spread.
New South Wales Rural Fire Service commissioner Shane Fitzsimmons said the teenager had been immediately stood down from his firefighting duties.
“Our members will be rightly angry that the alleged actions of one individual can tarnish the reputation and hard work of so many,” Fitzsimmons said.
“This type of alleged behaviour is the ultimate betrayal of our own members, and of the broader community.”
Six people have been killed, hundreds of homes destroyed and more than 1.5 million hectares (3.7 million acres) scorched across Australia since early October.
Dozens of fires were still burning on Wednesday, including 129 in New South Wales. Large swathes of the state were facing “high” or “severe” fire danger conditions.
More than 1,800 firefighters were battling those blazes, 66 of which were uncontained.
Several people have been arrested in recent weeks for deliberately lighting fires, including a 51-year-old man accused of sparking a huge blaze in an attempt to protect his cannabis crop.