Farah's victory in the 5,000m in the Luzhniki Stadium in Moscow was his fifth world or Olympic gold medal and made him only the second man in the world ever to win the double-double after Ethiopian great Kenenisa Bekele.
An exhausted-looking Farah, who also took the title in the 10,000m event on Saturday, knelt down and kissed the ground after storming over the finish line.
He also won the 5,000m and 10,000m at last year's Olympics and the 5,000m at the World Championships in Daegu in 2011.
Following his victory, a clearly elated Farah walked around the track with a Union flag draped over his shoulders before jumping up in the air in excitement and raising his arms above his head in his signature "Mobot" pose.
Smiling and waving at fans, he then made his way to where his wife Tania and daughter Rihanna were sitting in the crowd, hugging them both as hundreds of camera bulbs flashed in his face.
He told the BBC: "I never thought in my career I would achieve something like this. This is something I've worked so hard for. All I was thinking about was my kids and how much I've been away from them."
He said he found the race, which saw him stay behind at first before powering to the front in the final laps, a lot harder than the earlier event. "It was hard," he said. "It was a lot more hard work than the last, I put so much hard work into it."
Farah also thanked his team and the public for the support they had given him. "I had a lot of pressure but, at the same time, I enjoy it," he said. "I'm very proud to represent my country and hold the Union Jack."
His wife said she felt "overwhelmed" by his win. Mrs Farah, who is also mother to the couple's year-old twins Aisha and Amani, told ITV News: "The pressure going into this race was phenomenal. It was a nerve-wracking experience for us to watch that."
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