Thomas Keating, 22, had pleaded guilty to reckless driving over the death of Emily Jayne Collie, 20, on the resort island of Phuket last month.
On Thursday, the Phuket Provincial Court handed Keating a one-year suspended sentence and a fine of 5,000 Thai baht (Â£115; $144).
He will now be able to leave Thailand.
Ms Collie suffered fatal neck and shoulder injuries when the pair collided on separate rented jet skis.
At the time, Keating told police his vision was impaired by sunlight reflecting off the water.
"I respect the judge's decision, and am grateful that the sentence was suspended," said Mr Keating said in a statement.
"This was a very difficult process for meâ€¦ but the heartbreak that Emily's parents, Ian and Sallie Collie, are going through right now is infinitely and incomparably more difficult."
Ms Collie's parents have said they "do not believe anybody was at fault" in the collision.
Keating had been barred leaving the country until his trial was finished.
An Australian man has received a suspended jail sentence over a jet ski collision that killed his girlfriend in Thailand.