Tom Davies, 19, raised his arms in triumph after crossing the finish line in Battersea, south London. He was roared home by around 100 family, friends and others who have followed his exploits on his blog.
Tom has fled monkeys, been chased by dogs in Albania, and raced an emu in Australia during his six-and-a-half months in the saddle.
He was overcome with emotion after stepping off his bike at the end of the challenge.
He said: “I’ve just cycled around the world! It’s the best feeling.
“It’s been a lot of pain, a lot of suffering, so it’s amazing to finish.”
Battling wind, rain and snow, Tom notched up 100 miles of cycling a day to complete his trip, and raised more than £58,000 for charities.
The money will go to Prostate Cancer UK Carney’s Community, which works with disadvantaged young people, and the Sohana Research Fund, set up to support Sohana Collins, 13, who suffers from Recessive Dystrophic Epidermolysis Bullosa, or RDEB.
Nicknamed the Butterfly Disease, this is an incurable and often fatal illness which causes the skin to badly blister.
Tom broke down in tears as he said: “I met Sohana herself and it’s just inspirational what she goes through every day.
“I’ve had a hard seven months but she puts up with it her whole life.”
Tom plans to study materials engineering at Loughborough University later this year.
He spent years preparing for his journey, and while the Guinness Book of Records have not verified that he is the youngest ever person to complete the trip, it is believed he could be.