Thomas was born on October 6, 1923 in London, England. He was the son of Americans, Lowell Thomas Sr., a prominent writer, broadcaster, and traveler, and Frances "Fran" (née Ryan) Thomas. In 1949, Thomas and his father were invited by the Tibetan government to make a film there with the hope that their reports would help persuade the U.S. government to defend Tibet against the Chinese. The trip lasted 400 days, and the father and son were the last Westerners to reach Lhasa before the Chinese invasion and occupation. CBS did not broadcast the resultant film, Expedition to Lhasa, Tibet, until years later, but his book about the expedition, Out of This World, published in 1950 became a bestseller