The 27-year-old, who has cerebral palsy, made light work of the stifling Rio heat to storm home in a world record time of 1.00.43, adding to the 100m title she had already accrued.
“This is my preferred event and I knew there was lots of expectation on me, so to win it under that pressure feels amazing,” said Hermitage. “Everyone was expecting me to win and I did feel the pressure.
“It’s also because of my age I’m more aware of how everything is such a big deal. I’m getting better at coping though.”
Hermitage quit athletics while still a teenager but returned to the sport after being inspired by London 2012, and has already set her sights on future success.
“The London 2017 world championships will be my London 2012 and that’ll be the real test,” added Hermitage, who could win a third gold when she competes in tomorrow’s 4 x 100m relay.
Team-mate Stephen Miller, meanwhile, a three-time Paralympic champion, required a season’s best throw of 31.93 m to claim bronze in the F32 club throw.