"The Good Place" star served as a radio presenter in her native U.K. prior to becoming an actress, but working off-camera didn't stop haters from attacking her for her appearance.
And Jamil reveals she looked to Clarkson, who has struggled with her changing figure over the years, for inspiration in how to handle the rough period with grace.
"I remember you going through that (fat-shaming), and then very shortly afterwards, I gained a lot of weight back home in England," she shared with Clarkson on her self-titled U.S. talk show.
"I was a radio DJ, by the way, you couldn't even see me; people just wanted to know I was thin over the airwaves!" Jamil exclaimed.
She continued, "So I got nationally fat-shamed for six months in my own country, and it was your response to yours (tough time) that gave me the strength to get through mine."
Jamil has since become a leading voice in the body neutrality movement, a new drive for women's empowerment, which centres around the concept that people don't need to be focused on their figures or praised for their bodies.