Gates won the spot back from Mexican telecom mogul Carlos Slim Helu, who had topped the list for the past four years. His Gates' net worth is estimated at $76 billion, according to Forbes.
Helu comes in second with $72 billion, followed by Spanish clothing magnate Amancio Ortega, known for the Zara retail chain, with $64 billion.
Warren Buffett ranked fourth, with $58.2 billion, followed by Larry Ellison of Oracle with $48 billion.
The number of billionaires in the world have hit a new record, according to Forbes, with 1,645 on the list and 268 newcomers.
The U.S. still has the most billionaires, with 492, and the largest net worth gainer was Mark Zuckerberg of Facebook, who was ranked 21 on the list. He more than doubled his fortune to $28.5 billion as the value of Facebook stock soared.
The Associated Press contributed to this report.