Officers in Tullamore, County Offaly are investigating the blaze which occurred at a house in Rhode late last night.
The incident occurred between 11.30pm and 1.50am at a house at Coolcur in Rhode, authorities said.
A 24-year-old man was seriously injured during the blaze. Emergency services were called and he was rushed by ambulance to Tullamore Hospital.
He has since been transferred to St James's Hospital in Dublin for treatment. Reports suggest he also suffered stab wounds before the house was set ablaze.
The victim is believed to have escaped the house and was found by a passer-by at the rear of the secluded property.
His condition is described as critical. Gardai have received no reports of anyone else injured in the incident.
The scene has been preserved for a Technical examination and investigations are ongoing.
Witnesses are asked to contact Tullamore Garda station on 057 0327600, the Garda Confidential Line on 1800 666 111 or any Garda station.