He was probably the son of Nicholas Forman of Hutton in Berwickshire, and Jonet Blackadder. Forman had three brothers, John and Adam who were both knights – Adam was the standard-bearer to King James IV at the Battle of Flodden and John was the king's serjeant-porter who was captured at the battle – and Robert who was dean of Glasgow cathedral. He also had two known sisters—Isabel, the second wife of Sir Patrick Home of Fast Castle and an unnamed sister whose son, John Roul, became commendator of May after Forman's death. A possible third sister, Jonet Forman the Prioress of Eklis (Eccles), is the first named in a letter of protection and respite (similar to a will) dated 28 March 1513, when Forman lists a number of his kith and kin. He was educated at the University of St Andrews graduating as a Licentiate of the Arts in 1483.