Downey plays Atomic Energy Commission head Lewis Strauss, a key figure in the the United States' effort to build and later deploy a nuclear weapon towards the end of World War II.
Some call Downey the likely favorite to win the Oscar after coming away with awards for supporting actor at the Golden Globes, British Academy Film Awards (BAFTA) and Screen Actors Guild (SAG) Awards.
Nominated twice in 2009 for Tropic Thuder (Supporting) and in 1993 for Chaplin (Leading), Downey has the opportunity to take home his first Oscar at the 96th Academy Awards.
"Oppenheimer" received a total of 13 nominations including best picture. Co-star Cillian Murphy is up for Best Actor in a Leading Role for his performance as Robert J. Oppenheimer.
"Oppenheimer" continued to steamroll through Hollywood's awards season on Saturday, winning the top prize, for outstanding cast, along with awards for Cillian Murphy and Robert Downey Jr., at the 30th Screen Actors Guild Awards.
March 10 is Oscar Sunday! Watch the 2024 Oscars live on ABC.
Red carpet coverage starts at 1 p.m. ET | 10 a.m. PT with "Countdown to Oscars: On The Red Carpet Live." At 4 p.m. ET | 1 p.m. PT, live coverage continues with "On The Red Carpet at the Oscars," hosted by George Pennacchio with Roshumba Williams, Leslie Lopez and Rachel Brown.
Watch all the action on the red carpet live on ABC, streaming live on OnTheRedCarpet.com and on the On the Red Carpet Facebook and YouTube pages.
The 96th Oscars, hosted by Jimmy Kimmel, begins at 7 p.m. ET | 4 p.m. PT, an hour earlier than past years.
The Oscars are followed by an all-new episode of "Abbott Elementary."