Molly Maybe won bronze for Ireland in the 200m breaststroke at the European Youth Olympics in Baku on Wednesday.
Mayne swam 2:30.76 behind Justine Delmas of France in second and winner Evgeniia Chikunova of Russia.
"It feels great," the Templeogue swimmer said after the race.
I'm so happy. It's all I've wanted.
I went out efficient and controlled trying to build into the wall a little bit. My coach said my turns were the quickest so I tried to keep that.
On the third 50m, I saw the girl next to me in lane two. I knew she was on my feet. I tried to get power out of every kick and gave it my all.
That felt amazing. At first, I thought I was fourth and then I looked again and saw I got the bronze. I was just so happy.
Mayne will go in the 100m breaststroke tomorrow.
The medal was Ireland's second of the festival. On Tuesday evening, Rhasidat Adeleke won 100m gold.
Photo by Eóin Noonan/Sportsfile