Clymer was orphaned in 1740, only a year after his birth in Philadelphia. A wealthy uncle reared and informally educated him and advanced him from clerk to full-fledged partner in his mercantile firm, which on his death he bequeathed to his ward. Later Clymer merged operations with the Merediths, a prominent business family, and cemented the relationship by marrying his senior partner's daughter, Elizabeth, in 1765.