Manning was born in Saint John, New Brunswick, and attended Kings College in Halifax, Nova Scotia. As did his two older brothers, Manning signed up to participate in WWI, but he was too young - when the War ended, he was still in training, and never saw action overseas. He signed his attestation papers for the RFC on 14 May 1918.
In the 1920s he moved to the United States, living initially with his great uncle, Craven Langstroth Betts, the noted Canadian poet. In the US, he lived in Manhattan before moving to Staten Island in 1928, where he began writing short stories for several pulp science fiction magazines. After teaming with SF writer Fletcher Pratt in "City of the Living Dead" in the May, 1930 issue of Science Wonder Stories, he wrote "The Voyage of the 'Asteroid'", which appeared in the Summer 1932 issue of Wonder Stories Quarterly, and The Man Who Awoke, a series of stories that was later published as a novel. He also translated at least one German-language story for Hugo Gernsback's magazines (this may have been the translation of his popular story "The Man Who Awoke," published as Der Jahrtausendschläfer (The Millennium Sleeper). However, In the July, August and September, 1932 issues of Wonder Stories appeared "In the Year 8000", by Otfrid von Hanstein, translated by Manning, teamed with Konrad Schmidt.
Manning lost his two older brothers at very early ages: the oldest Frederick Charles died of wounds suffered fighting for the 85th Battalion, C.E.F in the battle of Vimy Ridge, France, on April 9, 1917; James Harold suffered wounds in the same battle but survived the war. He died working as an engineer for the Standard Oil Company in Maturin, Venezuela, in October, 1924 at age 27. It is possible the loss of these brothers and the horrors of war the country had just endured caused Laurence to become interested in the idea of Utopia. In the early 1930s he had over 500 books in his collection on the subject. It was in hopes of obtaining more book titles on Utopia that Manning contacted Wonder Stories magazine. He hoped to talk with Hugo Gernsback, but instead got David Lasser. They formed a strong friendship that lasted until Manning's death in 1972. They ate lunch together frequently, and it was at one of them that Manning mentioned having an idea for a story. After some discussion, Lasser suggested that Manning contact Fletcher Pratt, who could help with the story. This resulted in Manning's first published science fiction work, co-written by Pratt, entitled City of the Living Dead, which appeared in the May, 1930 Science Wonder Stories.
Manning gave up his successful writing career at the end of 1935 (with the exceptions of "Coal Thief" in the April, 1936 The Planeteer and "Expedition to Pluto" in the winter, 1939 Planet Stories), and devoted his time to Kelsey mail order nursery business he owned and managed. Apart from several short stories in the 1950s (Good-Bye, Ilha!, Mr. Mottle Goes Pouf, Men on Mars), he never wrote any more science fiction. However, he was the author of a successful book on gardening, The How and Why of Better Gardening (1951), Van Nostrand & Co, used for more than 40 years as a textbook by the Garden Clubs of America.
He was a founding member of the American Interplanetary Society, serving as both president and editor of the Society's publication, Astronautics. For his involvement in the Society, Manning is recognized by the Smithsonian's National Air and Space Museum as an early rocketry pioneer. It was during his tenure as president of the society that the organization's name was changed to the American Rocket Society. Manning retired from the Society in the mid-1940s, stating that rocketry had 'grown up', and was no longer a place for amateurs. In 1960, Manning was awarded a fellowship in the Society, presumably given at the Society's annual meeting.
Manning married Edith Mary Finette Burrows in 1928 and had three children: Helen Louise, Dorothy, and James Edward. His daughter Dorothy has mentioned that Laurence was not only a skilled writer, but a pianist as well. He composed his own pieces, primarily as Music Director of his church, though only one, Peter Pan, was ever published. He also smoked pipe. He lived in Highlands, New Jersey, from 1951 until his death in 1972.