The 48-year-old actor earned an estimated $75 million from June 2012 to June 2013, according to Forbes magazine's annual list of highest paid actors.
Most of the 'Iron Man 3' star's earnings came from starring in 'The Avengers', as his contract saw him receive a percentage of the film's total earnings at the box office.
The movie is the third highest-grossing film of all time and earned $1.5 billion worldwide.
Robert beat off stiff competition from Channing Tatum, 33, who made $60 million.
Most of the actor's profits came from his role in 'Magic Mike', which he and director Steven Soderbergh independently financed and produced.
'Les Miserables' star Hugh Jackman came third on the list, bringing home $55 million after a successful year, just ahead of Mark Wahlberg, 42, who earned $52 million.
Dwayne 'The Rock' Johnson rounded out the top five with $46 million from his roles in 'Fast & Furious 6' and 'G.I. Joe: Retaliation', which were both huge hits at the box office.
Others in the top 10 included Leonardo DiCaprio, Adam Sandler, Tom Cruise, Denzel Washington and Liam Neeson.
In compiling the list, Forbes considers factors including upfront pay, profit participation, residuals, endorsements and advertising work.
Forbes' top 10 highest earning actors from June 2012 to June 2013:
1 - Robert Downey Jr.
2 - Channing Tatum
3 - Hugh Jackman
4 - Mark Wahlberg
5 - Dwayne 'The Rock' Johnson
6 - Leonardo DiCaprio
7 - Adam Sandler
8 - Tom Cruise
9 - Denzel Washington
10 - Liam Neeson