A volunteer firefighter who died when his truck rolled while fighting a major blaze south west of Sydney has been remembered as a selfless father with an "unbelievable" love for his brigade.

Key points: Andrew O'Dwyer's father described him as a "free spirit"

Andrew O'Dwyer's father described him as a "free spirit" Mr O'Dwyer loved his fire brigade, Captain Darren Nation said

Mr O'Dwyer loved his fire brigade, Captain Darren Nation said He was posthumously awarded the Commissioner's commendation for extraordinary service and bravery

Andrew O'Dwyer, 36, was killed alongside his colleague Geoffrey Keaton, 32, at the Green Wattle Creek fire near Buxton when the truck he was travelling in rolled off the road on December 19.

Three other firefighters from the Horsley Park Rural Fire Brigade were injured.

Mr O'Dwyer's father Errol on Tuesday told a service at Our Lady of Victories Catholic Church his son was a wonderful, sweet boy who found a second family when he joined the Rural Fire Service (RFS).

"He was a free spirit who lived in the present and on his terms," Mr O'Dwyer said.

Andrew considered his greatest achievement his 19-month-old daughter Charlotte, Mr O'Dwyer said, who he loved madly along with his wife Melissa.

Mr O'Dwyer was posthumously awarded the Commissioner's commendation for extraordinary service and bravery — the highest accolade that can be given to NSW firefighters.

RFS Commissioner Shane Fitzsimmons gives Mr O'Dwyer's service medal to his daughter. ( AAP: Dean Lewins )

The 36-year-old was also a talented photographer who used an Instagram account to show the world his brigade.

Brigade Captain Darren Nation said the young father relished being a mentor and trainer.

"The love he had for the fire brigade was as thick as the blood that ran through his veins," Mr Nation said.

Charlotte O'Dwyer, the daughter of Andrew O'Dwyer, stands in front of her father's casket wearing his helmet after being presented with her father's service medal. ( AAP: Dean Lewins )

Mr Nation said Mr O'Dwyer, one of his closest mates, was the kind of man who would sacrifice his own life for someone else if it came down to it.

"My friends, that is a rare and beautiful person," he said.

A haka is performed at the funeral of NSW RFS volunteer Andrew O'Dwyer. ( AAP Image/Dean Lewins )

"I will never, ever have another Andrew."

Prime Minister Scott Morrison hugs Horsley Park RFS captain Darren Nation at the funeral of Andrew O'Dwyer. ( AAP: Dean Lewins )

Commissioner Shane Fitzsimmons said Horsley Park was one of the state's best functioning brigades and this was largely thanks to men like Mr O'Dwyer who took such pride in their volunteering.

Mr Keaton, whose son Harvey was born just days apart from Mr O'Dwyer's daughter, was laid to rest at a service last week.