The 65-year-old Couric revealed the diagnosis on Instagram.
"Every two minutes, a woman is diagnosed with breast cancer in the United States," Couric wrote. "On June 21st, I became one of them."
In an essay on her website, Couric wrote that she received the cancer diagnosis on her wedding anniversary. She said she underwent a surgical procedure in July, and began receiving radiation treatments in September.
Her final treatment was Tuesday.
Couric said she decided to share her diagnosis and details of her treatment to urge others to undergo screening.
"Please get your annual mammogram. I was six months late this time. I shudder to think what might have happened if I had put it off longer," she wrote. "But just as importantly, please find out if you need additional screening."
Couric's first husband, Jay Monahan, died of colon cancer at age 42 in 1998.
(Reporting by Dawn Chmielewski in New York; Editing by Lisa Shumaker)