On a sweaty, sticky night in the Bird's Nest, Bolt was out of the blocks quicker and opened up an unassailable lead over the first 100m before coming away down the straight and jabbing his thumbs at his chest as he crossed the line.
His 19.55 seconds was the fastest in the world this year, his speed and peerless championship class too good for American Gatlin, whose 19.74 was well outside his season's best.
Jamaican Bolt, who will also compete in the 4x100m relay, said: "It means a lot to me.
"I'm happy to be a 10-time World Championships gold medallist, especially when people have been saying I would lose.
"I had the utmost confidence. As long as my coach is confident, I'm super confident.
"The British people give me a lot of love and I will continue running fast."
South Africa's Anaso Jobodwana set a national record of 19.87, with Panama's Alonso Edwards three thousands of a second behind in fourth.
Britain's talented 20-year-old Zharnel Hughes, who trains with Bolt in Jamaica, ran a personal best of 20.02 for fifth in his first major final.
But this was all about the man metres in front, his 10th world gold just another astonishing number in a career without parallel.
For much of this season Bolt, 29, has been a struggling shadow of the man who has dominated both sprinting and his sport for the past seven years.
Coming into these championships he had raced only one 200m all summer, and that a lacklustre 20.13 in May.