By 1394, Donnchadh, Earl of Lennox had presented him with control of the hospice of the poor at a place called "Poknade". By the beginning of the 15th century Walter's involvement in Lennox facilitated his role as the castellan of Dumbarton. In either 1397 or 1398, Walter seized the castle after the death of his brother Robert.
By 1394, Donnchadh, Earl of Lennox granted Walter control over a hospice for the poor at "Poknade". By the start of the 15th century, Walter's involvement with Lennox led to his appointment as the castellan of Dumbarton. In either 1397 or 1398, Walter seized Dumbarton Castle after the death of his brother Robert.