The 17-year-old scored 330.70 in Kiev to finish ahead of Russian duo Anna Chuinyshena (326.90) and Iuliia Timoshinina (313.30).
"To be honest, I did not expect this victory," said Toulson. "I am not totally satisfied with my dives yet."
The World Championships take place in Budapest, Hungary from 14 July.
Toulson is expected to compete both individually and with Tonia Couch in the synchronised event.
Britain's Lois Toulson won European Championship gold in the 10m platform as she finalises her preparations for next month's World Championships.