The stone - weighing 1,098 carats - was shown to President Mokgweetsi Masisi, two weeks after the diamond firm, Debswana, unearthed it.
The huge gem is only slightly less heavy than the world's second-largest diamond which was also found in Botswana in 2015.
"This is the largest diamond to be recovered by Debswana in its history of over 50 years in operation," said Lynette Armstrong, Debswana Diamond Company's acting managing director.
Debswana is a joint venture between the government and global diamond giant De Beers and up to 80% of the income from sales goes to state coffers through dividends, royalties and taxes.
Botswana's Minerals Minister, Lefoko Moagi, said the latest find could not have come at a better time for Botswana after the pandemic caused diamond sales to slump last year.
The biggest diamond ever discovered was the 3,106 carat Cullinan diamond found in South Africa in 1905 and the second largest is the 1,109 carat Lesedi La Rona found in Botswana in 2015.