As a child he was fostered for some time into the household of Richard Siward, the prominent banneret knight of Walter's eldest brother William.

In 1240 Walter was delegated command of his brother Gilbert's campaign in west Wales, and was responsible for ending Welsh power in Pembrokeshire and Ceredigion.

Knowing this, Walter fled to Wales immediately after his brother's funeral and put his castles in defence, so that royal custodians could not take them over.

The king is said to have vented a lot of pent-up anger on the Marshal family, but relented and allowed Walter's officers to legally occupy the castles.

[4] Earl Walter made a point of dutifully following the royal court for several months after his rehabilitation, and promptly answered the summons for the king's campaign in Gascony in the summer of 1242, supplying ships and knights.

Walter's widow, Margaret received a full dower third from the Pembroke earldom and lordships, including the county of Kildare in Ireland.

Her dower was larger than the individual holdings of the 13 eventual co-heirs of the Marshal estate after Ansel's subsequent death.