The celebrated actress -- who's countless accolades over her 25-year span as a performer include an Oscar for her role in 2003's Monster -- was honored with the Career Achievement Award at the star-studded awards show, and she spoke to ET's Lauren Zima backstage at the Beverly Hilton Hotel, where she opened up about the overwhelming experience.
"Nicole Kidman just gave me an award for something that I never really, you know, I never thought that I would have this career," Theron said, getting emotional with appreciation. "And that's really the truth."
"I think every actor always longs for longevity," she continued. "We try to stay in this game for a long time and the fact that I've been able to do that, not only for this long but on my own terms, and make the stuff that really matters to me, that means a lot."
Theron added, "The fact that I can really look back on my life and feel like I did something that I really wanted to do means a lot."
She also felt incredibly lucky to be presented the award by Kidman -- who showered Theron with praise during the ceremony.
"She, to me, is such an icon and somebody that I so respect and admire," Theron marveled. "For her to say all of those things and for us to finally be in a film together -- and not just a film, [but] something that I'm incredibly proud of that I think is incredibly important and to share that with her -- means a lot."
During the awards show, Theron was brought to tears by Kidman's kind words about her work ethic and her dedication. Theron returned the compliments in kind, thanking Kidman for her unending support and shared that Kidman's stellar performances have had a profound impact on her own career.
Before the show, Theron spoke with ET on the red carpet, where she reflected on the film she felt had the biggest impact on her career.
"I mean, it's hard -- they really are like your children. But I think Monster was definitely a moment in my career where I realized the opportunity that I was given was a chance to show that I was capable of more and it did change my career," Theron said of the film, in which she played real-life sex worker-turned serial killer, Aileen Wuornos.
Theron said that, before Monster, she'd mostly be relegated to playing "a lot of wives and a lot of girlfriends," but that her powerhouse turn as Wuornos showed what she was truly capable of.
"After that, I didn't have to fight so hard for those interesting parts anymore, and more opportunities came my way to get outside of my comfort zone and do things that were maybe not expected for me," she continued. "I think from that moment on, I built a career that has kind of defined what I really wanted my career to be -- not typecast, not stereotypical roles, but to really do things that are interesting and challenges the psyche of how we look at people."
Theron and Kidman's highly-anticipated new biographical drama Bombshell-- co-starring Margot Robbie, Kate McKinnon, Alice Eve, John Lithgow and Mark Duplass, and directed by Jay Roach -- hits theaters Dec. 20.
-- Additional reporting and observations by Nikki Snook.