The 35-year-old is being recognized for her range as an actress -- she taken on comedy, drama, musicals and animated -- and for delighting the MTV audience throughout her 20-year career. MTV President Stephen Friedman called Witherspoon "one of the most versatile and accomplished performers of her time."
Witherspoon has won more than 30 awards, including an Oscar, a Golden Globe, a BAFTA, a SAG award and multiple MTV Movie awards. She will now join previous Generation Award winners Sandra Bullock, Ben Stiller, Adam Sandler, Mike Myers, Tom Cruise and Jim Carrey.
While MTV chose the Generation Award winner, fans voted online for the winners of all other categories, including best kiss, best villain, best fight and best line from a movie.
"Saturday Night Live" star Jason Sudeikis will host the MTV Movie Awards at the Gibson Amphitheater. Among those set to present are Ryan Reynolds, Blake Lively, Steve Carell, Shia LaBeouf, Cameron Diaz, Selena Gomez and Nicki Minaj.
The Associated Press contributed to this report.