Upon the death of his brother John de Vesci in 1289, William succeeded to the family estates, including as Lord of Sprouston in Scotland.

Sir John FitzThomas, 4th Lord Offaly, fiercely quarrelled with William over rival claimants of the King of Connaught.

King Edward I summoned all the parties to Westminster, however, FitzThomas did not appear, and although William requested for a judgment in his favour by reason of the default, this was not allowed, with the matter finally being resolved during the parliament in August 1295.

William also resigned Malton Castle and his Yorkshire estates to Antony Bek, Bishop of Durham, however, he received them back for life and entailed after his death on his illegitimate son and his heirs.

He also placed in charge of Alnwick Castle to Antony Bek, Bishop of Durham on trust, to restore it to his illegitimate son when he became of age.

They had issue: He also fathered an illegitimate son, William de Vescy of Kildare, with Devorgille, daughter of Donal Roe MacCarthy Mór, Prince of Desmond.

During the lifetime of his brother, John, William bore arms blazoned: Or, a cross Sable, debruised by a label of five points Gules.