Tiernan Darnton, 20, is accused of killing Mary Gregory in a fire at her home on Levens Drive in the town in May 2018.
The 94-year-old was taken to hospital following the blaze but died on June 1 2018.
Her cause of death was given as pneumonia and smoke inhalation.
An initial joint investigation by police and the fire service concluded the fire started as the result of a discarded cigarette and an inquest in October 2018 concluded Mrs Gregory’s death was an accident.
Following further information given to police in May 2019 a new investigation led by the Force Major Investigation Team was launched and Tiernan Darnton was arrested on suspicion of Mrs Gregory’s murder and subsequently bailed.
Further enquiries led officers to conclude the fire had in fact been started deliberately.
Following a lengthy and complex police investigation, and after consultation with the Crown Prosecution Service, Darnton, of Heaton Road, Lancaster, has today been charged with murder.
He is due to appear before Blackpool Magistrates’ Court tomorrow (Wednesday, March 10)
In a tribute Mary’s family said: ““Mary was a much loved mother and grandmother to us, and she has been sadly missed every day since her death.
“It has been very hard for us to come to terms with the tragic circumstances of her death.
"As a family we need to understand the truth about the circumstances which led to her death, to allow us to come to terms with her passing as best we can. We ask people to respect our privacy at this difficult time.”