Mayweather fought twice in the last 12 months and his combined pay was $85 million before reporting to prison to serve an 87-day term for a domestic abuse conviction.
Forbes said that Mayweather's knockout of Victor Ortiz last September and a unanimous decision over Miguel Cotto in May accounted for the income he collected from June 2011 to June 2012.
Pacquiao also fought twice in the last year and picked up $62 million, which is second on Forbes' list of the Top 100 earners among sports figures in the last year.
The boxers unseated Tiger Woods, who had been the leading earner since 2001. Woods is third this year at $59.4 million, which was about $16 million less than 2011.
Tennis star Roger Federer is fifth with earnings of $52.7 million, just ahead of basketball's Kobe Bryant ($52.3 million). Golf's Phil Mickelson comes in at No. 7 with $47.8 million followed by soccer's David Beckham ($46 million) and Cristiano Ronaldo ($42.5 million). Peyton Manning of the NFL completes the Top 10 at $42.4 million.
Maria Sharapova, the top-ranked women's tennis player, is the highest woman on the list with earnings of $16.6 million coming in 26th.
Forbes says it includes earnings from salaries, bonuses, prize money appearance fees, licensing and endorsement income in determining its list.