Mollie Hughes, 26, who is based in Edinburgh, reached the summit of Everest (8,848m) from the north side on Tuesday.
Her feat also makes the climber the youngest European woman and the first English woman to scale the peak from both the north and south sides.
In temperatures as low as minus 40C, Ms Hughes who is originally from Torbay, Devon, reached the summit at 1.14am GMT (5.34am local time in Nepal) with climbing partner Jon Gupta of Mountain Expeditions.
She hopes to raise more than £8,000 for Cancer Research UK, £1 for every metre climbed and is being supported throughout the expedition by Tiso where she works in Edinburgh
After reaching the summit, Ms Hughes said: “I am elated, exhausted and know I still have the hardest part to do - the long and difficult descent to base camp. Jon (Gupta) and I have already spent more than four weeks acclimatising on the mountain.
“Thanks to a weather window, yesterday evening we left Camp 3 (8,300m) and we’ve finally reached the top.
“The climbing has been really, really hard but our mental and physical strength got us up here.
“I can confirm that the north side is definitely more difficult than the south side.”
She added: “Huge thanks to Jon, the sherpas, family, friends and to Tiso as my principle sponsor on this expedition. I am really proud to be the youngest Briton to have scaled Everest from both sides - and to have raised funds to support the work of Cancer Research UK.
“Now, we’ll focus on achieving a safe descent from the top of the world.”
Ms Hughes, who in 2012 reached the summit of Mount Everest from its south side at the age of 21, has been periodically posting video clips during her record-breaking ascent.
A soundtrack by Britney Spears plays in one of the clips taken in tent as Gupta reveals that a Rubik’s cube is among the items carried by the pair to test their mental alertness at altitude and to keep occupied during rest periods.
The route includes an arduous and psychologically testing final day ascent over three prominent rocky steps on the north east ridge.
All are negotiated at an altitude of over 8,500 metres (28,000ft) in the so-called “death zone”.
Chris Tiso, CEO of Tiso Group and who was part of the 2000 Tiso expedition on which Polly Murray became the first Scottish woman to summit Mount Everest, said: “Mollie Hughes is an inspirational young woman.
“All at Tiso Group are very proud that she has reached the summit after a long and difficult climb and entered her name in the Everest record books.
“It is a phenomenal achievement.
“Of course, Mollie and Jon (Gupta) now face an equally daunting descent. All involved with the Tiso Return to Mount Everest 2017 Expedition wish them a safe return to base camp and look forward to welcoming Mollie home in early June.”
Ms Hughes left the UK for Kathmandu in Nepal in early April before travelling into Tibet and hopes to return to the UK in early June.