Show producers Craig Zadan and Neil Meron made the announcement today.
Fonda will add some more prestige to the Oscar ceremony. She's earned a whopping seven nominations and picked up acting trophies for her roles in "Klute" and "Coming Home."
Washington co-starred in Quentin Tarantino's Best Picture nominee "Django Unchained," and currently stars on ABC's hit drama "Scandal." Garner, who recently appeared in "The Odd Life of Timothy Green," will be seen next in "Dallas Buyers Club."
"Marvel's The Avengers" cast members Robert Downey Jr., Samuel L. Jackson, Chris Evans, Jeremy Renner and Mark Ruffalo are also participating.
Returning 2011 Oscar winners Jean Dujardin, Christopher Plummer, Octavia Spencer and Meryl Streep will also hand out awards, as will the reunited cast members of "Chicago," Richard Gere, Queen Latifah, Renée Zellweger and Catherine Zeta-Jones.
The evening's performers include Kristin Chenoweth, Jennifer Hudson, Catherine Zeta-Jones, Hugh Jackman, Russell Crowe, Anne Hathaway, Amanda Seyfried, Eddie Redmayne, Samantha Barks, Aaron Tveit and Helena Bonham, Adele, Dame Shirley Bassey, Norah Jones and Barbra Streisand.
The Academy Awards air live on ABC Sunday, February 24.