Pittman, who ran a personal best of 54.14secs in her semi-final, was unable to match that performance but still won comfortably in 54.40secs.
World junior champion at both the 400m flat and hurdles two years ago, it was confirmation of the 19-year-old's arrival on the senior stage.
Debbie-Ann Parris of Jamaica took the silver medal in 55.24secs while there was an unexpected bronze for Canada's Karlene Haughton.
England's Natasha Danvers was three metres clear of Haughton in third place but clipped the final hurdle with her lead leg and tumbled to the ground.
It was a desperate moment for the World Student Games champion, who picked herself up to finish seventh, just behind Scotland's Sinead Dudgeon.
"I was so ready mentally and I so wanted to bring that medal home," said a devastated Danvers.
"I was really visualising it and told myself to attack, but the technical beat me there."
Jamaica's 1996 Olympic champion Deon Hemmings, who won the second semi-final, did not start in the final.