Johnson-Thompson, 26, secured the title with a convincing win in the 800 metres, the last of the seven disciplines.
Her time of 2:07.26 seconds saw off the challenge of the defending champion Nafissatou Thiam. Johnson-Thompson and the Belgian had effectively annexed the competition.
Going into the 800 metres, Johnson-Thompson boasted 5,976 points. Thiam lurked menacingly on 5,839. Verena Preiner on 5,579 points was an irrelevance to the duel.
Johnson-Thompson's win will allow her to exorcise the demons from her two previous visits to the world championships.
In 2015 in Beijing, she failed all three attempts for the long jump and slumped in form to come fifth on home soil in London in 2017.
"The last two world championships, mid-heptathlon, I've gone back to my hotel and cried and cried for hours when things have gone badly," she said.
"Those were the low points of my career. Rio Olympics, as well. I've had a lot of bad years. I'm just so happy I came out in front for a change."
In Doha, she was resplendant. She claimed personal best performances in four events and set a British record of 6,981 points to inflict a first defeat on Thiam since May 2016.
Kaul's rise to the ascendance was facilitated by the withdrawal of the world record holder Kevin Mayer.
The 27-year-old Frenchman, who was leading the field after seven rounds, succumbed to an achilles injury as he attempted to take part in the pole vault.
"I have to accept it," said Mayer. "At least it happened here and not at the Olympics."
Going into the 1500 metres, the last of the 10 events, Kaul was in third place behind the Canadian, Damian Warner, and the pacesetter Maicel Uibo.
But Kaul trounced the pair. He claimed the race in 4:15.70 seconds, more than 16 seconds faster than the Estonian and 25 seconds ahead of Warner.
His haul of 841 points catapulted him into first place and he finished with 8,691 points to secure his country's first gold of the championships.