Carrie is the only female to land a nod for the top prize this year, and Miranda thinks it's important she is recognised with the first win for a woman since Taylor Swift lifted the award eight years ago.
Sharing photos of herself and Carrie performing on Instagram, Lambert writes: "Currently being on tour with all female artists, I've been thinking a lot about all the work that goes into what we do...".
"She (Underwood) put out her first single in 2005 and from then on country music was changed for good. That iconic voice has been classin' up our stages, charts and televisions for a decade and a half. The Voice. The legs. The songs. The brand. The mom. The wife... The Jesus lover. The blonde bombshell that is Carrie. She blows me away every time I hear her sing".
"She never wavers in who she is or what she stands for. She has stayed true & pushed herself to be better. If you have never heard her sing 'How Great Thou Art' do yourself a favor and listen. I have her back in this picture and I'll always have her back. So for the sake of sequins, spanx and spray tans, take it home! You Carrie the torch!".
Underwood, who was nominated in 2016, will find out if she's a winner on 13 November, when she goes up against Keith Urban, Garth Brooks, Eric Church, and Chris Stapleton for the Entertainer of the Year trophy.