The 26-year-old Aussie from Townsville stood on the top step of the MotoGP™ podium for the first time in five years and the first time as a factory Ducati rider on Sunday.
Miller, who started from third on the grid at Jerez, reeled in early leader Fabio Quartararo (Monster Yamaha) and kept it pinned to take the chequered flag.
His teammate Francesco Bagnaia crossed the line in second place, completing the Ducati team’s first 1-2 since 2018.
“I just tried to do what I could,” Miller said with tears in his eyes after the race.
“I knew I had a bit of a gap behind me and if I could get past Fabio – I could see he was struggling – get past him, get my head down, make no mistakes and just try to punch out the laps.
“Those last seven or eight laps were the longest of my career.
“I mean, it’s just indescribable what I’m feeling right now, it’s a flood of emotions – happy, sad, everything.
“I wish my parents were here to celebrate it with me but they’re back at home, I know they’ll be celebrating.
“I want to thank everyone for all their support, I’ll try do it again soon.”
The win was Miller’s first in the premier class since the 2016 Dutch TT on a Marc VDS Honda.
“I can’t thank Ducati enough for giving me this opportunity,” added Miller, who was promoted from Pramac Ducati to the factory team for the 2021 season.
“Wearing these colours is a dream come true for me, and it means a lot.
“Thank you, Gigi (Dall’Igna), Paolo (Ciabatti), Davide (Tardozzi), Claudio (Domenicali) and the whole team for having always believed in me.”
Miller is sixth in the MotoGP™ standings with 39 points, while Bagnaia leads the World Championship with 66 points.