The "highly significant" oil and deep gas resource is thought to dwarf the Gulf kingdom's current reserves, according to an official announcement on Sunday.
It is located in the Khaleej al-Bahrain basin, located off the country's west coast.
"Initial analysis demonstrates the find is at substantial levels, capable of supporting the long-term extraction of tight oil [light crude] and deep gas," said Bahrain's minister of oil, Shaikh Mohammed bin Khalifa al-Khalifa.
The reserves were discovered during the last three months of 2017 after Bahrain intensified its search for new fossil fuel deposits.
Crown Prince Salman bin Hamad tweeted that a press conference on Wednesday would "provide additional details on the discovery, including initial findings of size and extraction viability".