Swift won artist of the year at the fan-voted show on Tuesday in Los Angeles, beating out Drake, Ed Sheeran, Imagine Dragons and Post Malone for the top prize.
"This award and every single award given out tonight were voted on by the people, and you know what else is voted on by the people," she said, "the midterm elections on November 6."
Swift announced on Sunday that she was voting for Tennessee's Democratic Senate candidate Phil Bredesen, breaking her long-standing refusal to discuss anything politics.
Voting was a hot topic at the AMAs. Host and Golden Globe-winning "black-ish" actress Tracee Ellis Ross wore a shirt that said, "I am a voter," and comedian-actor Billy Eichner told the audience, "The biggest election of our lifetime is happening."
"Please grab your friends and tell them to vote. Now is the time. If you believe in equality for women, for people of color, for the LGBTQ community. If you believe that climate change is real and that we need to do something about it," he said onstage before presenting an award.
"And you can go to Vote.org like Taylor Swift told you to," he added.
Swift kicked off the AMAs with a performance of "I Did Something Bad," while Cardi B picked up the night's first award, favorite hip-hop/rap artist, which she dedicated to her daughter.
"I really want to thank my daughter," said Cardi B, who gave birth to Kulture Kiari Cephus in July. "I gotta prove people wrong. They said I wasn't going to make it after I had a baby."
The rapper hit the stage to give a festive and colorful performance of her No. 1 hit, "I Like It," where she was joined by J Balvin and Bad Bunny, who was wheeled onstage inside a shopping cart. Cardi B's husband, Offset of the rap trio Migos, danced along in the audience with group member Quavo as Cardi B worked the stage with vibrant dance moves, including the salsa.
Cardi B returned the favor, screaming happily when Migos was named favorite pop/rock duo or group, beating out Maroon 5 and Imagine Dragons, later in the show.
"We did not know we was winning this at all," said Quavo, also giving a shout-out to group member Takeoff, who didn't attend the AMAs.
"I want to thank you sexy lady," Offset said, pointing to Cardi B.
Like Cardi B's performance, rising newcomer Ella Mai also won over the crowd when she sang the year's biggest R&B hit, "Boo'd Up," starting the performance as she walked down the aisle of the Microsoft Theater. Khalid, Quavo and Offset were some of the audience members dancing along, while others sang and some even filmed her with their phones.
Others who shined onstage included R&B singer Ciara, who showed off her skilled dance moves and was joined by a fierce Missy Elliott. Carrie Underwood was in perfect form vocally, and Camila Cabello — who won new artist of the year — gave a heartful, touching and vocally impressive performance of the ballad "Consequences," earning her a standing ovation.
The three-hour show closed with a rousing tribute to Aretha Franklin, who died in August. Gladys Knight, Ledisi, Mary Mary, Donnie McClurkin and CeCe Winans were among the musicians who paid tribute to the Queen of Soul's gospel roots and her iconic album, "Amazing Grace."
Rapper-singer XXXTentacion, who was fatally shot in June, was also honored: He won favorite soul/R&B album for his 2017 debut, "17." It was days after he was named best new artist at the BET Hip-Hop Awards.
His mother, Cleopatra Bernard, said she was honored to accept the award on behalf of her son. "I'm so nervous," Bernard said as the audience cheered her on.
Post Malone, who wore a baby blue suit and performed, won favorite pop/rock male artist, Underwood was named favorite country female artist, Khalid picked up favorite soul/R&B male artist, and Kane Brown won favorite country male artist.
Other performers included Mariah Carey, Jennifer Lopez, Shawn Mendes and twenty one pilots.