The songstress also took home the coveted Female Artist of the Year Award.
Morris won the award for her song "The Bones," which she co-wrote along with Jimmy Robbins and Laura Veltz, and accepted the trophy on behalf of all of them at the Opry House in Nashville.
"This is really bittersweet because I didn't write this by myself," Morris said. "Each time I've been so lucky to accept an award for this song, my co-writers Laura Veltz and Jimmy Robbins have not gotten a chance to say anything."
Given the COVID-19 safety protocols throughout the year, shows have either been conducted virtually, or with significantly limited capacities, often with those performing being the only guests in attendance.
"I so wish they could be here," an emotional Morris shared. "But thank you to the ACMs for keeping us safe."
While holding the trophy, Morris added that the honor "is so meaningful to me."
"Song of the year is something that I've just dreamt of for so long and I feel like with this song, with 'The Bones,' when I wrote it -- I was dating my now husband [Ryan Hurd] and it was just a song to him," she said. "I feel sometimes like songs know you better than you know them at the time, and I feel like this song has revealed so many new things to me that I didn't know were possible the day I wrote it, and this has just been a hell of a year."
"Hopefully country music and maybe even this song brought you and your family and friends some peace, so thank you so much," she concluded.
Morris spoke with ET's Rachel Smith after her win where she dished about the evolution of her hit single.
"It's a bit of an older song for me in my life, but it has taken on a lot of depth in the years, it's sort of like a fine wine, it's aged in meaning and in sound," she shared. "So yeah, that kind of hit me tonight on stage just accepting the award for Song of the Year because it's just crazy when your songs sometimes know you better than you know them and this song definitely knew me in a deeper way."
Earlier in the evening, Morris and her husband performed together for the first time at any awards show, belting out a beautiful rendition of "Chasing After You."
Toward the end of the show, Morris won big once again when she took home the award for Female Artist of the Year, beating out Carly Pearce, Kelsea Ballerini, Miranda Lambert and Ashley McBryde.
"I feel really, really just happy to be in a category with women that were not able to tour this year but brought so much heat to the game, to country music this year," Morris shared during her acceptance speech. "You have inspired me so much, to no end."
"Even in a year where no one has gotten to play shows, I have heard some of the best music out of all of you this past year," she added. "So thank you so much for inspiring me."
Morris continued her praise of her fellow nominees after accepting her award, telling ET, "I hope they're all celebrating tonight because they turned in a banner year of work, and I'm a huge fan of all of theirs."
ET caught up with Morris and Hurd ahead of Sunday's award show where they opened up about performing together for the first time. For Hurd, it wasn't only his first performance with his wife, but his first time on the ACMs stage.
"This is my first ever opportunity to perform at the ACMs, so that for me is really cool and to get to do it with Maren, is even better and it kinda takes all the pressure off it," Hurd shared. "I don't know if that adds pressure or takes it off, but I don't feel very much right now."
For the new mom, having her husband on stage means she doesn't have to scan the crowd to lock eyes with Hurd, since he's right there with her.
"I'm so excited, because typically I'm trying to find him in the crowd if I'm on stage performing," Morris explained. "I like having somebody that I can make eye contact with, and now it's like super easy to find him cause he's on stage with me."