Born in Somerset to a wealthy family, Lethbridge was educated at Trinity College, Cambridge, during the course of which he attended an expedition to Jan Mayen island, becoming part of the first group to successfully climb the Beerenberg.

In his capacity as Keeper of Anglo-Saxon Antiquities at the Cambridge University Museum of Archaeology and Ethnology, Lethbridge carried out excavations at sites around Britain.

Finding geology to be "crushingly dull", he rarely attended lectures and took little interest in his studies, instead spending much of his time shooting, fishing, and sailing.

[11] Although initially planning to travel independently, they decided to join a Norwegian expedition led by Hagbord Ekerold and accompanied by Swiss mountaineer and glaciologist Paul Louis Mercanton.

[12] The expedition set sail from Bratvaag aboard two ships in August 1921, and upon arriving at Jan Mayen they became the first team to successfully climb the Beerenberg ('Bears Mountain').

[16] In summer 1923 Lethbridge was part of a second expedition led by Wordie, designed to explore the eastern coast of Greenland to conduct geological and archaeological investigations and repeat Edward Sabine's pendulum gravity experiments.

With food reserves running low, the crew resorted to killing and eating grey seals and polar bears, before they eventually aborted the mission and returned home.

[21] In turn, Lethbridge derided the archaeological establishment, being frustrated by how long it took them to accept what he deemed to be "facts", and trusting his instinct and common sense rather than the dogma of the profession.

[22] Over the course of his career at the museum, Lethbridge produced 60 archaeological reports, written in an unusually informal manner that used humour and wit and included narrative descriptions of the excavation process.

[37] As the Second World War loomed, the British Admiralty commissioned Lethbridge to undertake a reconnaissance mission to Iceland to analyse German naval activity around the country, which he carried out in summer 1939.

[39] As war broke out, Lethbridge organised the transfer of much of the museum's collections to Balsham Caves for safe keeping, while also becoming a warden of the Air Raid Precautions.

But the couple found life on Kerrera too isolated and soon returned to Cambridge,[43] despite Lethbridge's dislike of the place and most of the university staff whom he worked alongside.

[46] In January 1948, Lethbridge received word that his son Hugh had died by suicide after suffering post-traumatic stress disorder during his time in the armed forces.

[50] That same year, Thames and Hudson published Lethbridge's Boats and Boatmen as part of their "The Past in the Present" series edited by archaeologist Jacquetta Hawkes.

[52] As part of his increasing public profile, the BBC invited him to give the third talk in their second series of Myth or Legend?, which he devoted to the question of whether Europeans had arrived in the Americas prior to Christopher Columbus; in particular he looked at the claims that St. Brendan and Thorfinn Karlsefni had made the journey across the Atlantic.

[53] Over several seasons he also carried out excavations of wheelhouses at South Uist, and on one occasion was visited at the site by Queen Elizabeth II and Prince Philip, Duke of Edinburgh.

[57] The Council for British Archaeology brought together a committee to assess Lethbridge's findings, composed of I. W. Cornwall, W. F. Grimes, Christopher Hawkes, and Stuart Piggott.

[62] Relocating to Branscombe in east Devon, he and Mina set up home in Hole House, a fortified building that dated to the Early Modern period,[63] and angered some of the locals by banning fox hunters from crossing his land.

[64] Lethbridge came to believe that Hole House was haunted, describing unexplained noises and smells there; this increased his interest in the paranormal, and he decided to devote much of his time to investigating such phenomena in what he deemed to be a scientific manner.

[69] He followed this work with Witches – Investigating an Ancient Religion (1962), which articulated a form of Murray's witch-cult hypothesis but also contained many digressions and anecdotes unrelated to that topic.

[75] In both his books and private letters from this period he regularly ranted against modern life and society, while in other correspondences with individuals in the United States he championed the authenticity of the Kensington Runestone and Westford Knight.

Echoing many of the claims made by Erich von Däniken in Chariots of the Gods (1968), Lethbridge argued that the late prehistoric stone circles of the British Isles had been beacons for extraterrestrial spacecraft.

[82] As the Branscombe house was owned by the Lethbridge Family Trust, Mina was obliged to move out after her husband's death, and she sold his belongings out of financial necessity.

[83] Mina also collected together Lethbridge's unfinished book with the help of writer Colin Wilson; together they assembled it into publishable form and it was brought out by Routledge in 1976 as The Power of the Pendulum.

Archaeologist Niall Finneran asserted that Lethbridge had a "distinguished if fairly unspectacular reputation" within British archaeology prior to his adoption of fringe theories.

[86] Various colleagues expressed critical praise of his work in this field; for instance, Lethbridge's fellow Anglo-Saxon archaeologist Audrey Meaney noted that his "observations on features in the cemeteries he excavated around Cambridge were perspicacious but in advance of his time".

[89] On his death, Glyn Daniel described Lethbridge as "a colourful, stimulating, provocative and often controversial figure in British archaeology", who represented "one of the last of that invaluable band of dilettante scholars and devoted amateurs of whom we have had so many in Britain".

[85] An anonymously authored obituary in The Antiquaries Journal referred to "the strength and honesty of Lethbridge's character as a man, and the singleness of purpose that united all his work, as experimental testing of what he found by observation", seeing these as the unifying characteristics behind his divergent research interests.

[90] According to the historian Ronald Hutton, as a result of both his unorthodox ideas and his "contempt for professionalism in all fields", Lethbridge's "status as a scholar never really rose above that of an unusually lively local antiquary".