The saw-scaled viper is one of the deadliest snakes in the world and is often found close to towns and cities in south Asia.
Vets from South Essex Wildlife Hospital rescued the reptile after a stonemason, who had ordered the rocks, tried to identify the reptile and immediately called the nearby animal hospital for help.
A charity spokesperson said: “In addition to many British wildlife species coming in today we also had a call about a critter that is definitely not in the country it should have been.
“We had a call regarding a stowaway snake that had arrived in a shipping container from India.”
Experts said the species is thought to have killed more people than all others combined.
Founder and manager, Sue Schwar, said the people who opened the crate and found the viper were “very lucky to be alive”.
“The snake was probably cold from travelling, so was not too active,” she told the BBC.
“Having had one before we understood fully the gravity of just how dangerous these reptiles are.”
The snake is being stored in a room where the door has been taped up with warning signs.
“We are glad not to have to deal with venomous creatures too often but feel sad for the snake that we can’t give it is freedom and get it back home,” the charity added.