The 'Southbound' singer accept the prestigious award on stage, sans audience, wearing a sparkling Marina Hoermanseder Fall 2020 gown and Cirari jewels.
"Thank you, God, so much. All Glory, glory to God," she said while collecting her award. "And thank you to the ACMs, not just for this, but for putting me in such incredible company. I am more than happy to share this with Thomas Rhett and just to have my name mentioned with his."
Later backstage, the 37-year-old old realized she forgot to thank her husband, Mike Fisher, and their two sons, Isaiah Michael, 5, and Jacob Bryan, 19 months, during her heartfelt acceptance speech.
"I'm a dummy for not mentioning my husband or my children in my acceptance speech," she told reporters. "You would think after this many years and seeing other people give speeches and doing some of my own, I would think of people who are important to me. So I'm sorry! I do love my children and my husband!"
Underwood's big moment was the first time in ACM history that the highest honor of the evening had two winners. Earlier in the ceremony, the Oklahoma native marked the 95th anniversary of the iconic Grand Ole Opry by honoring trailblazing female country stars with a special performance.
"They are some of my heroes, and I am so honored to stand alongside them as a fellow member of the Grand Ole Opry," she said on stage. "It's my pleasure to pay tribute to these legendary ladies as we celebrate the Opry's 95th anniversary."
The American Idol winner then performed a medley hits by country queens, including Patsy Cline's 'Crazy,' Loretta Lynn's You Ain't Woman Enough,' Barbara Mandrell's 'I Was Country When Country Wasn't Cool,' Dolly Parton's 'Why'd You Come in Here,' Reba McEntire's "The Night the Lights Went Out in Georgia" and Martina McBride's "A Broken Wing."
The 2020 ACM Awards was originally planned to air on April 5 in Las Vegas, Nevada, but was postponed and relocated due to the ongoing COVID-19 pandemic. Hosted by Keith Urban, the live show also featured performances from the likes of Taylor Swift, Luke Bryan, Eric Church, Luke Combs and Tim McGraw.