The British star, who did the distance double at London 2012, needed all of his famed final-lap speed as he repeated the feat in Russia to cement his place in the pantheon of sporting greats.
Defending champion Farah, 30, was put under pressure on the final lap of the 12-and-a-half-lap race but his turn of speed saw him lead his rivals home to win in 13 minutes 26.98 seconds.
That means he is the only man apart from the peerless Kenenisa Bekele to hold the Olympic and World Championship distance double simultaneously.
“It was hard – a lot harder work than last year,” Farah said afterwards. "I never thought I would achieve something like this. It was so tough but thankfully I've come through it with another gold medal.
"I've worked so hard for this and I was just thinking about my kids and how much I've been away from them and I wanted this for them.
"Of course I felt tired after the 10,000m. I wanted to run as easy as possible today. I thought the Kenyans would work as a team and might want to box me in, but it didn't happen. I was able to go in front and control the race.
"I know I have a fast time in the 1,500m, so I was confident about my finish.
“I’m very proud to represent my county and hold the Union Jack.”
Silver went to Ethiopian Hagos Gebrhiwet (13:27.26), who should be lauded for a ferocious challenge down the back straight, while Kenyan Isiah Kiplangat Koech was also part of that group but had to settle for bronze despite setting the same time.
It is Farah's fifth global title after he claimed the longer distance crown last Saturday. He won silver in the 10,000m in Daegu.
In a final of muddling and erratic pace, the trio of Ethiopians and Kenyans did their best to disrupt the Briton with team tactics but Farah, towards the back early on, went to the front with three laps to go.
With his principal rivals for gold, all with fresher legs after not running in the 10,000, queuing up to pass at the bell, Farah gritted his teeth, pumped his arms faster and refused to yield.
Koech appeared the main danger around the final bend but did not have the legs to get past as Farah held him at bay all the way to the line and Gebrhiwet's late burst snatched silver by one thousandth of a second.