The snake measuring 17ft 7in (5.18m) and weighing 164lb (74kg) was found in Everglades National Park, the University of Florida announced.
The python – now dead – was pregnant with 87 eggs, also believed to be a record.
Non-native Burmese pythons have been blamed for a staggering decline of mammals in Florida’s Everglades.
Scientists say the latest discovery shows just how pervasive the snakes – native to South East Asia – have become in South Florida.
“It means these snakes are surviving a long time in the wild,” said Kenneth Krysko, at the Florida Museum of Natural History.
“There’s nothing stopping them, and the native wildlife are in trouble.”
He said that the snake had feathers in its stomach that would help to identify the types of wildlife it was eating.
“A 17-and-a-half-foot snake could eat anything it wants,” he added.
Pythons kill their prey by coiling around it and suffocating it.
They have been known to swallow animals as large as deer and alligators.
After scientific investigation, the snake will be exhibited at the museum on the University of Florida campus for five years before being returned to the Everglades National Park.