The cub, who is only four to six weeks old, was found near Redding in California earlier this week after the Zogg Fire burned through the area on 27 September, killing four people.
Weighing just 1.7kg (3.75lb), the cub was taken to Oakland Zoo where veterinarians are treating his injuries.
They have named him Captain Cal, after the California Department of Forestry and Fire Protection's mascot, and said he is reacting well to treatment.
The cub was badly burned, especially his paws, and his whiskers were completely singed off by the fire and he had severe eye irritation.
After being cleaned up and given antibiotics, supportive fluids, pain medication and kitten milk formula through a syringe, things are looking up.
Vets said X-rays confirmed he has no damage to his lungs or bones.
Dr Alex Herman said the cub is eating on his own and "acting feisty - both promising signs for his recovery".
She added: "Unfortunately, a lion this size is too small to be released back into the wild, but we are hopeful that under the zoo's care, it will get a second chance as an ambassador for its species.
"We're cautiously optimistic that this cub will now survive and thrive, our dedicated team at Oakland Zoo is fully committed to do everything we can for him and for his beautiful species."
In the wild, mountain lion cubs stay with their mothers until they are around two years old to learn the skills they need to survive on their own.
As Captain Cal will not be able to learn those skills, Oakland Zoo said he will be placed "in a suitable forever home" once he is well.
He is the 13th mountain lion to be rescued for Oakland Zoo by the California Department of Fish and Wildlife.
The lions are facing numerous threats in California, including increasing wildfires, but they are often hit by cars and illegally poached.