Adelson was born into a poor family and grew up in the Dorchester neighborhood of Boston, Massachusetts, the son of Sarah (née Tonkin) and Arthur Adelson.[6][7] His family was of Ukrainian Jewish ancestry.[8][9] His father drove a taxi, and his mother ran a knitting shop
He started his business career at the age of 12, when he borrowed two hundred dollars from his uncle and purchased a license to sell newspapers in Boston.[11] At the age of 16, he had started a candy-vending-machine business. He attended trade school to become a court reporter and subsequently joined the army.[12] Adelson attended City College of New York, but soon decided to drop out.
He established a business selling toiletry kits after being discharged from the army then started another business named De-Ice-It, which sold a chemical spray to help clear frozen windshields.[13] In the 1960s, he started a charter tours business.[6] He had soon become a millionaire, although by his 30s he had built and lost a fortune twice. Over the course of his business career, Adelson has created over 50 of his own businesses