An adventurer has made history by completing a marathon swim from Land's End to John O'Groats.

Sean Conway, 32, left Cornwall on 30 June, swimming along the west coast.

Every year thousands of people attempt to walk, cycle or run the journey between Land's End and John O'Groats, a distance of 874 miles (1,407km) by road.

Conway completed the final mile of his journey by sea on Monday, making him the first person to swim the length of the UK.

Born in Zimbabwe but now living in the south of England, Conway said he undertook the challenge because people doubted it could be done. He has raised thousands of pounds for the War Child charity in the process.

He swam around 10 miles a day and slept on a yacht or in accommodation onshore. The initial plan was to complete the swim in two months but weather and injuries delayed the time it took.

He told BBC Breakfast: "No one's ever done it and that sort of got me thinking, considering Land's End to John O'Groats is such an iconic route. Then, as soon as people told me I was going to die or that is wasn't possible, I just thought: 'I'm going to prove you wrong'.

"The weather's been quite tough – big winds and big waves have slowed my progress a bit.

"Getting stung by jellyfish is quite tough. I've had to grow a ridiculous beard to shield my face and had to cover up with loads of Vaseline because every now and again I'd take a stroke and get a jellyfish right in the face and I don't know who gets more of a fright, me or it.

"We've lost kayaks at sea, rigs at sea and our boat has taken a bit of a hammering; we all took a bit of a hammering. The sea can be a nasty place."

Conway sets off from Land's End in June. Photograph: Artur Tixiliski/Cartel Photo/Rex

Conway began his involvement in endurance sports at the age of 10, with a mile-long swim across a lake, and competed in kayak marathons as a teenager. He has also climbed Mt Kilimanjaro dressed as a penguin, and cycled 16,000 miles through six continents in 116 days, much of it with a fractured spine, according to his website Sean Conway.

In a blog entry in late October, Conway detailed the tough experience of swimming in the far north of Scotland.

"Cape Wrath had taken its toll on us and for the first time I wondered if I had missed the weather window. Trying to swim along the north coast of Scotland in November (or near enough) was always going to be tough. I just didn't think it was going to be this hard," he wrote.

"We're now spending a few days recovering and waiting for some good weather."

Earlier in the month he described how the water temperatures plunged, turning one of his toes blue when it was submerged.

"Long-term fatigue is also a worry. I've had five days off in 40 days and I can really feel it in my body. I'm still under 10 stone and can't seem to repair quickly enough after each session. I really need a week off but that's just not possible right now," he wrote.

• This article was amended on 14 November 2013 because the original said Sean Conway swam "to the most northerly point of the UK mainland". Dunnet Head is the most northerly point, not John O'Groats.