Remmy Goulart was playing in the kitchen at her family's home on Brick Kiln Road in Falmouth, Massachusetts, just before 9am on Sunday when she was attacked.
Police said Reece retrieved a pistol from a nearby room, but realized it wasn't loaded.
Reece then grabbed a knife and started stabbing the dog to save his daughter from its jaws, fatally wounding the animal.
The Falmouth Fire and Rescue Department and Falmouth Police Department rushed to the home and began treating the injured girl.
Remmy was transported to the Falmouth Hospital by ambulance, and subsequently airlifted to a Boston area hospital by helicopter.
Shortly after the incident, Falmouth fire Lt Scott Stanbard told WBZ-TV the toddler's injuries were believed to be life-threatening.
The victim's relatives later revealed to Fox 25 that Remmy had three blood transfusions and underwent an hours-long surgery overnight to repair some of the damage.
Remmy will also require plastic surgeries in the the coming weeks.
Police said the family had owned the pit bull five years and it had no known history of aggression.
'At this time, the attack appears to have been unprovoked,' police said in a statement.
A GoFundMe was created to alleviate the costs of Remmy's medical expenses on her road to recovery.
'This family has been through a lot and we all want to be able to take financial stress away so they can focus on their beautiful baby,' the account read.
By Tuesday evening, the account had raised more than $27,000.
'You're all so amazing,' Remmy's father, Reece, wrote on the page dubbed 'Rally for Remmy'.
'My heart is full and I have no words. I'd die for my little girl. I can't thank you enough! I love you all,' he added.
Speaking to the Boston Herald, Susan Moran, chairwoman of Falmouth's Board of Selectmen, praised the father's 'heroic efforts' to minimize the injuries to his child.