The Plymouth College pupil clocked 1:00.54 to finish joint third with Greece’s Ilektra Lebl. Russia’s Polina Egorova won the race in 59.36 seconds, with Great Britain’s Amelia Clynes second in 1:00.12.
Stephens, 16, said: “I’m overwhelmed. I’m really happy with that swim. It was a PB, so I couldn’t have asked for much more. The bronze topped it off.
“I wasn’t expecting it, I went in sixth. I was thinking a PB would be good and then maybe climbing a couple of places to fifth or fourth, but when I saw third I was so happy.
On sharing bronze with Lebl she said: “It’s rare that happens, 100th of a second slower and I would have been off the podium, but I was pleased. I had no idea it was so close.”
Prior to Stephens’ medal-winning swim, Leander team-mate Joe Hulme, who had missed out on a medal in the 100m backstroke event earlier in the week by just two hundredths of a second, suffered more disappointment.
He narrowly missed out again in the 200m event, despite a personal best time of 2:00.16, which was half-a-second quicker than he had swam at the British Championships in April.
Hulme, who had gone into the final ranked third, ended up finishing fifth in a record-breaking race.
His GB team-mate Luke Greenbank won in a world junior record time of 1:56.89. Belarus’ Mikita Tsmysh was second in 1:59.46 and Russia’s Roman Larin was third in 1:59.60.
Meanwhile, fellow Leander swimmer Tom Fannon will be going for glory on Saturday in his favourite event, the 50m freestyle.
Fannon is the quickest athlete in the field with a season’s best time of 22.48 seconds.
The Plymouth Leander swimmer does already have a gold medal in his bag for being part of the successful Great Britain 4x100m freestyle squad. Although he did not swim in the final, he did compete in the heats, which qualified him for a medal. However, he will be looking to win one outright in the ‘splash and dash’.
Stephens is also set to return to the pool on Saturday in the 50m butterfly event.