Bolt, who overcame the doubters with his 100m victory Sunday, crossed the finish line in 19.55 seconds with Gatlin, previously the fastest man in the world this year over 200m, having to settle for another silver medal after clocking 19.74s.
South Africa's Anaso Jobodwana took home bronze after recording a time of 19.87s.
"It's great, a fourth [world title] win over 200m and it means a lot to me," Bolt told BBC Sport
. "I'm happy to be a 10-time World Championships gold medalist, especially when people have been saying I would lose.
"For me I knew I had the utmost confidence. As long as my coach is confident, I'm super confident. There was never a doubt that I would win this one. I'm number one."
Gatlin had been attempting to claim a first World Championship gold since winning both the 100m and 200m finals in Helsinki 10 years ago, but the American was left chasing Bolt's shadow as the Jamaican racked up his 10th world title.
Bolt and Gatlin were neck and neck going into the final 100m, only for the Jamaican to soon pull away and cross the finish line in style -- in the the pair's first meeting in the 200m since the 2005 World Championships final.
Upon embarking on his momentous victory lap, things did for a moment come to a crashing halt for Bolt, with the 29-year-old soon finding himself being taken out by a photographer on a segway.
That failed to stop the Jamaican, however, from getting back up to his feet with a smile on his face and continuing his lap of honor around the Bird's Nest track.
"He tried to kill me, I don't know what was going on," Bolt joked afterwards.
Battle for the soul of athletics
Both the 100m and 200m finals had been billed -- perhaps somewhat melodramatically -- as the battle for the soul of athletics. While double Olympic 100 meter champion and "fastest man ever" Bolt has never failed a drugs test, Gatlin has twice been banned for substance misuse.
Returning from the poor form and the pelvic injury that has hampered this year to win "was a big deal," he added.
Beating the form book again
Bolt, as he did in the 100m final in Beijing, is clearly a man for the big occasion.
The Jamaican, who holds the world record at 19.19s, clocked 19.95s in Wednesday's semifinal, while Gatlin looked in better shape with 19.87s.
The American also came into the race as comfortably the fastest man in the world this year over 200m, having clocked 2015's two fastest times with 19.57s -- his fastest ever over the longer sprint -- and 19.68s.
Gatlin had run more than two tenths of a second faster than any other man in the field this year, and almost half a second quicker than Bolt, who had seen his season been restricted by a pelvic injury, limiting him to just one 200m race before coming to China.
But Bolt 's imperious win leaves Gatlin with plenty of questions as to how he can beat the Jamaican when it comes to a final.