From a family with landholdings in the south of Lincolnshire, he was the son and heir of Thomas Moulton (died before 1198) and his wife Eleanor Boston.
After initial military service, he became a senior judge and held important government positions, in the process extending his inherited estates and accumulating considerable wealth.
[1] As a knight, he served in King John's forces in the Normandy campaigns of 1202–04, against Llywelyn the Great in Wales in 1211 and in Poitou in 1214.
In between, he obtained administrative posts, becoming sheriff of Lincolnshire from 1205 to 1208 and serving on royal enquiries in 1213 and 1214.
However, he made his peace with the new regime in 1217 and in 1218 was appointed an itinerant justice in the five northern counties.