The billionaire's firm already had a minority stake in BNSF and the move will give Berkshire Hathaway control of the 77.4 per cent of shares it did not own.
Of what is believed to be the biggest deal of his entire career, Mr Buffett said: "It's an all-in wager on the economic future of the United States.
"I love these bets."
BNSF is the biggest American transporter of goods such as corn and coal, while it also ships consumer products such as refrigerators and televisions across the US.
Berkshire Hathaway will pay $100 a share to take control of the company assuming BNSF shareholders vote through the move.
Last month, BNSF reported third quarter freight revenues of $3.49 billion, partly thanks to a decrease in fuel surcharges worth $725 million to the business.
By Asim Shah