Underwood and Rhett seemed equally taken aback after host Keith Urban announced the tie at the awards show held at the Grand Ole Opry House in Nashville, Tennessee, on Wednesday.
โKeith, what is happening right now?โ Rhett asked, astounded, before thanking his family.
There was a lot of anticipation for the show, which featured Taylor Swift making her first appearance at the ACMs in seven years.
In awards announced before the show aired, Rhett also won music video of the year, while Townes won new female artist of the year.
Underwood sang a tribute to iconic female Opry members, including Patsy Cline, Reba McEntire, Martina McBride, Barbara Mandrell, Loretta Lynn and Dolly Parton.