He earned a $275m (£205m) payday for his boxing match in August against UFC star Conor McGregor, who is number four on the U.S. business magazine's list.
No women have made it onto the list, with Serena Williams dropping out of the elite earners after taking time off due to pregnancy.
In 26th place is golfer Rory McIlroy, who amassed the bulk of his earnings through endorsements as $34 Million of $37.7 million reportedly came from that.
From left: Former US boxer Floyd Mayweather, Barcelona's Argentinian forward Lionel Messi, and Real Madrid's Portuguese forward Cristiano Ronaldo. Baseball (14 athletes), Soccer (9), Golf (5), boxing, tennis (4 each) and racing (3) also landed multiple stars in the top 100.
Though the list of leading athletes consists of players from 11 different sports, basketball takes over the list with a top score 40 NBA players among the top 100, up from 32 in 2017. Messi's annual salary and bonus exceeded $80 million, making him the highest-paid player on the pitch this year. Two American football players make the top ten, coming in ninth and tenth. Completing the top 10 were basketball's LeBron James (85.5), tennis's Roger Federer (77.2), basketball's Stephen Curry (76.9) and quarterbacks Matt Ryan (67.3) and Matthew Stafford (59.5).
Endorsement income from sponsorship deals fell slightly, by 1% to $877m. The top 100 earned United States dollars 3.8 billion, a 23 per cent jump over past year.