The One Last Time singer was seen kissing rapper and producer Miller during a date night in California last month (Aug16), but only went public with their relationship on Tuesday (06Sep16).
Alongside a snap of the pair laying on the floor with Ariana's legs wrapped around her The Way collaborator, the pretty brunette wrote: "Baabyyy."
Fans were quick to comment on the black and white photo, with one person writing: "Goals."
The singer attended the MTV Video Music Awards earlier this month (Sep16) but went solo on the red carpet. Asked by MTV pre-show host Charlamagne Tha God the whereabouts of her "boo" (boyfriend), Ariana slyly answered, "Being supportive. It's OK to be alone even when you have a boo."
She was later joined inside by Miller, who stood by her side as they gave a standing ovation to Beyonce following her Lemonade performance.
The new romance is the latest in a string of high-profile relationships for the 23-year-old star, who formerly dated The Wanted's Nathan Sykes, Australian actor Jai Brooks and rapper Big Sean.
Following his split from Ariana after an eight-month romance, Big Sean told Entertainment Tonight: "Man, you know, I don't plan relationships. They just happen. That's all it is. I'm just... I'm just living it. It's no, it's no God, it's no script. You know, we just out here doing what we doing. Feelin' it out. It's no mistakes in life, though only lessons."
Ariana added to V magazine of the split: "I'm good at making the best out of something. It also wasn't that hard for me, because we were friends. So it's chill."
Ariana's most recent romance was with Ricky Alvarez, from whom she split in July (16).