The Kentucky rapper, 24, was among the first on the red carpet outside the Prudential Centre in Newark, New Jersey.
He is also presenting the show, which celebrates the best music videos with its coveted “Moonman” astronaut trophies, alongside hip hop stars Nicki Minaj and LL Cool J.
During the official livestream, he said: “I am feeling the love. I am in a good mood. I am hungry, I am focused.”
Of his eight nominations at the event, Harlow added: “It means the world. I haven’t won a lot of awards yet. I am hoping to clean up tonight and bring it all home to Kentucky.”
Asked to describe his upcoming performance at the event in one word, he replied: “Unforgettable.”
Italian rock band Maneskin, who won the Eurovision Song Contest in 2021, were among the early winners after scooping the off-camera best alternative award.
Speaking on the carpet, frontman Damiano David was asked if that took the pressure of them and joked: “It makes it easier!”
Bassist Victoria De Angelis added: “I think the most important thing for us is of course the performance and to give our best. A great performance is what we are aiming for.”
Taylor Swift also made a surprise appearance, posing for the cameras wearing a jewel-encrusted mini-dress.
Her arrival was met with screams and chants of “Taylor, Taylor, Taylor!” from the crowd.
Brazilian singer and actress Anitta said all of her home country was talking about the event.
About her performance during the main show, she added: “I feel like it is a World Cup and I am about to play a game.”
On the carpet, Snoop Dogg, who is performing alongside Eminem, said: “I feel good to be here and to still be appreciated and loved after so many years, to have a proper presentation on stage, to be able to perform.
“To be able to just come out here and enjoy the evening, as a fan and a performer.”
Harlow walked the carpet wearing a Hermes suit while LL Cool J appeared to take inspiration from motorcycle culture with a leather jacket.
Lizzo made an entrance wearing a blue-black Jean Paul Gaultier gown and copious gold jewelry including a large lip ring.
Other stars who made an appearance ahead of the ceremony included K-pop girl group Blackpink, R&B singer Khalid and rising music star Tate McRae.
Harry Styles, Adele and Ed Sheeran are among the British stars in contention for the top awards.
They face competition from US heavyweights including Billie Eilish, Harlow and Lil Nas X at the annual ceremony.
Styles, Harlow and Doja Cat are the three frontrunners at this year’s event, with eight nominations each, closely followed by Drake, Kendrick Lamar and Lil Nas X, with seven.
Former One Direction star Styles is up for top awards including artist of the year, best album for his latest release Harry’s House, and video of the year for As It Was.
The 28-year-old megastar takes on fellow Briton Sheeran for artist of the year, in an American dominated category, which also includes Drake, Bad Bunny and Lizzo.
Harry’s House comes up against Eilish’s Happier Than Ever, Drake’s Certified Lover Boy and Adele’s high-anticipated 30 for album of the year.
Also vying for the coveted video of the year are Doja Cat, for Woman, Harlow and Lil Nas X, for Industry Baby, Olivia Rodrigo, for Brutal, and Taylor Swift, for All Too Well (10 Minute Version) (Taylor’s Version).
The latter, which features Stranger Things star Sadie Sink, went viral earlier this year after fans speculated the song is based on Swift’s break-up with actor Jake Gyllenhaal.
Honorary awards will go to The Red Hot Chili Peppers, who are due to receive the global icon award, and Minaj, who is expected to receive the Video Vanguard Award.